Vulnerability-Lookup

URL	Tags
https://github.com/jpadilla/pyjwt/security/adviso…	x_refsource_CONFIRM
https://github.com/jpadilla/pyjwt/commit/06573692…	x_refsource_MISC
https://github.com/jpadilla/pyjwt/releases/tag/2.14.0	x_refsource_MISC

Vendor	Product	Version	CPE status
jpadilla	pyjwt	Affected: >= 2.13.0, < 2.14.0	guessed

BREW-MCP-PROXY-CVE-2026-102265 (GHSA-8WJV-2P76-3863)

Vulnerability from osv_homebrew – Published: 2026-09-30 10:08 – Updated: 2026-09-30 10:08 – Source website

Summary

PyJWT: Uncaught RecursionError in jwt.decode() on deeply nested token header

Details

Package

pyjwt (PyPI)

Affected versions

tested & verified on: 2.13.0. Every version whose PyJWS._load() translates only ValueError is affected

Description

PyJWS._looad() (jwt/api_jws.py:337) splits the compact token, base64url decodes the header segment and hands it to json.loads() before _verify_signature() runs. The parse is wrapped in except ValueError as e: raise DecodeError(...). That is what makes the documented contract sufficient for untrusted input: except jwt.PyJWTError (or InvalidTokenError) around jwt.decode(token, key, algorithms=[...]).

CPython's JSON decoder raises RecursionError (a RuntimeError subclass, not a ValueError) once nesting crosses the native stack guard. That exception leaves _load(), then jwt.decode(), and matches no PyJWTError handlerr at all. No key and no valid signature are needed: the header is parsed first, so a single unauthenticated request with an unsigned token suffices.

Scope: the recursion threshold is ~65,000 nesting levels; below it the same input yields a clean DecodeError (a 346,800-byte flat header is rejected normally, so depth, not size, is the trigger). A token this large cannot ride in an Authorization header (rejected at HTTP field limits,431 under gunicorn), but body transport (RFC 7662 introspection style) is a standard pattern. Under Flask 3.1.3 / gunicorn 26.2.0 each crafted request returns HTTP 500 instead of 401 and writes a full traceback to the error log; the sync worker survives.

Proof of concept

Against any endpoint that validates a token from its JSON body with the documented pattern:

import base64, json, http.client

def b64url(b): return base64.urlsafe_b64encode(b).rstrip(b"=")

# unsigned token: the header segment is 200,000 nested '[' (266,681 bytes total)
token = (b64url(b"[" * 200_000) + b"." + b64url(b'{"a":1}') + b"." + b64url(b"x")).decode()

conn = http.client.HTTPConnection("127.0.0.1", 8125, timeout=30)
conn.request("POST", "/api/protected", body=json.dumps({"token": token}),
             headers={"Content-Type": "application/json"})
print(conn.getresponse().status)   # 500, expected 401

Determinism: 20/20 crafted requests returned 500 against the reference container (PyJWT 2.13.0, Flask 3.1.3, gunicorn 26.2.0, Python 3.14.7) in 0.12 s (about 6 ms per request in a tight loop, 14 ms for a cold request), each leaving a RecursionError: Stack overflow ... while decoding a JSON array traceback in the error log.

Impact

An unauthenticated attacker can turn every request to a JWT validating endpoint into a server error with a full traceback logged per request, a cheap and repeatable denial of service on the authentication path (no crash, no data exposure).

Fix

Catch RecursionError alongside ValueError in _load() and raise DecodeError, or parse the header with a nonrecursive, depthbounded parser.

Reproduction

A standalone package (docker-compose.yml, Dockerfile, requirements.txt, target app, driver) accompanies this report:

cd <package dir>
docker compose up -d --build
python3 poc_check_then_attack.py
docker compose down -v

poc_pyjwt_recursion.zip

Exit 0= reproduced (control checks green, exactly one crafted request returns 500, traceback verified in docker logs, service alive afterwards); 1 = not reproduced; 2 = checks failed, no attack sent. The package's run_log.txt documents a complete proof run.

Credits

@Nivid42

Maintainer update — 2026-09-09

We reproduced the reported behavior on PyJWT 2.13.0: a deeply nested JSON array in the untrusted compact-JWS header reaches json.loads() before signature verification and raises RecursionError, which is not a PyJWTError. The same input is accepted by the public jwt.decode() path and can escape an application's normal except PyJWTError handling.

The fix is committed as 06573692ebcdec8831c3927513b3e87c31fbbb62. PyJWS._load() now translates both ValueError and RecursionError from header JSON parsing into DecodeError. A regression test covers the deeply nested-header path before signature verification. The full suite passes with 373 tests and 4 intentional cryptography-environment skips.

No release containing the fix has been published yet, so the patched version remains unset pending release planning. The advisory remains medium severity and unpublished.

Maintainer update — 2026-09-11

The verified fix for this advisory is included in PyJWT 2.14.0, released on 2026-09-11 and available on PyPI. PyJWT 2.14.0 is the first release containing the fix. This advisory is now published with 2.14.0 recorded as the patched version.

Severity

5.3 (Medium)


                    
                      CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

References

URL

Type

	https://github.com/jpadilla/pyjwt/security/adviso…	WEB
	https://nvd.nist.gov/vuln/detail/CVE-2026-102265	ADVISORY
	https://github.com/jpadilla/pyjwt/commit/06573692…	WEB
	https://github.com/jpadilla/pyjwt	PACKAGE
	https://github.com/jpadilla/pyjwt/releases/tag/2.14.0	WEB

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": null,
        "range_state": "affected",
        "resource": "pyjwt",
        "resource_purl": "pkg:pypi/pyjwt@2.13.0",
        "upstream_fixed_in": "2.14.0"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "mcp-proxy",
        "purl": "pkg:brew/mcp-proxy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.12.0_1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/pyjwt@2.13.0",
        "name": "pyjwt",
        "resource": "pyjwt",
        "strategy": "registry",
        "subject_version": "2.13.0"
      }
    ]
  },
  "details": "## Package\n\npyjwt (PyPI)\n\n## Affected versions\n\ntested \u0026 verified on: 2.13.0. Every version whose `PyJWS._load()` translates only `ValueError` is affected\n\n## Description\n\n`PyJWS._looad()` (`jwt/api_jws.py:337`) splits the compact token, base64url decodes the header segment and hands it to `json.loads()` before `_verify_signature()` runs. The parse is wrapped in `except ValueError as e: raise DecodeError(...)`. That is what makes the documented contract sufficient for untrusted input: `except jwt.PyJWTError` (or `InvalidTokenError`) around `jwt.decode(token, key, algorithms=[...])`.\n\nCPython\u0027s JSON decoder raises `RecursionError` (a `RuntimeError` subclass, not a `ValueError`) once nesting crosses the native stack guard. That exception leaves `_load()`, then `jwt.decode()`, and matches no `PyJWTError` handlerr at all. No key and no valid signature are needed: the header is parsed first, so a single unauthenticated request with an unsigned token suffices.\n\nScope: the recursion threshold is ~65,000 nesting levels; below it the same input yields a clean `DecodeError` (a 346,800-byte flat header is rejected normally, so depth, not size, is the trigger). A token this large cannot ride in an `Authorization` header (rejected at HTTP field limits,431 under gunicorn), but body transport (RFC 7662 introspection style) is a standard pattern. Under Flask 3.1.3 / gunicorn 26.2.0 each crafted request returns HTTP 500 instead of 401 and writes a full traceback to the error log; the sync worker survives.\n\n## Proof of concept\n\nAgainst any endpoint that validates a token from its JSON body with the documented pattern:\n\n```python\nimport base64, json, http.client\n\ndef b64url(b): return base64.urlsafe_b64encode(b).rstrip(b\"=\")\n\n# unsigned token: the header segment is 200,000 nested \u0027[\u0027 (266,681 bytes total)\ntoken = (b64url(b\"[\" * 200_000) + b\".\" + b64url(b\u0027{\"a\":1}\u0027) + b\".\" + b64url(b\"x\")).decode()\n\nconn = http.client.HTTPConnection(\"127.0.0.1\", 8125, timeout=30)\nconn.request(\"POST\", \"/api/protected\", body=json.dumps({\"token\": token}),\n             headers={\"Content-Type\": \"application/json\"})\nprint(conn.getresponse().status)   # 500, expected 401\n```\n\nDeterminism: 20/20 crafted requests returned 500 against the reference container (PyJWT 2.13.0, Flask 3.1.3, gunicorn 26.2.0, Python 3.14.7) in 0.12 s (about 6 ms per request in a tight loop, 14 ms for a cold request), each leaving a `RecursionError: Stack overflow ... while decoding a JSON array` traceback in the error log.\n\n## Impact\n\nAn unauthenticated attacker can turn every request to a JWT validating endpoint into a server error with a full traceback logged per request, a cheap and repeatable denial of service on the authentication path (no crash, no data exposure).\n\n## Fix\n\nCatch `RecursionError` alongside `ValueError` in `_load()` and raise `DecodeError`, or parse the header with a nonrecursive, depthbounded parser.\n\n## Reproduction\n\nA standalone package (docker-compose.yml, Dockerfile, requirements.txt, target app, driver) accompanies this report:\n\n```\ncd \u003cpackage dir\u003e\ndocker compose up -d --build\npython3 poc_check_then_attack.py\ndocker compose down -v\n```\n[poc_pyjwt_recursion.zip](https://github.com/user-attachments/files/31614987/poc_pyjwt_recursion.zip)\n\nExit 0= reproduced (control checks green, exactly one crafted request returns 500, traceback verified in `docker logs`, service alive afterwards); 1 = not reproduced; 2 = checks failed, no attack sent. The package\u0027s `run_log.txt` documents a complete proof run.\n\n## Credits\n\n- @Nivid42\n\n## Maintainer update \u2014 2026-09-09\n\nWe reproduced the reported behavior on PyJWT 2.13.0: a deeply nested JSON array in the untrusted compact-JWS header reaches `json.loads()` before signature verification and raises `RecursionError`, which is not a `PyJWTError`. The same input is accepted by the public `jwt.decode()` path and can escape an application\u0027s normal `except PyJWTError` handling.\n\nThe fix is committed as `06573692ebcdec8831c3927513b3e87c31fbbb62`. `PyJWS._load()` now translates both `ValueError` and `RecursionError` from header JSON parsing into `DecodeError`. A regression test covers the deeply nested-header path before signature verification. The full suite passes with 373 tests and 4 intentional cryptography-environment skips.\n\nNo release containing the fix has been published yet, so the patched version remains unset pending release planning. The advisory remains medium severity and unpublished.\n\n## Maintainer update \u2014 2026-09-11\n\nThe verified fix for this advisory is included in PyJWT 2.14.0, released on 2026-09-11 and available on PyPI. PyJWT 2.14.0 is the first release containing the fix. This advisory is now published with 2.14.0 recorded as the patched version.",
  "id": "BREW-mcp-proxy-CVE-2026-102265",
  "modified": "2026-09-30T10:08:19Z",
  "published": "2026-09-30T10:08:19Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/security/advisories/GHSA-8wjv-2p76-3863"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-102265"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/commit/06573692ebcdec8831c3927513b3e87c31fbbb62"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/jpadilla/pyjwt"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/releases/tag/2.14.0"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "PyJWT: Uncaught RecursionError in jwt.decode() on deeply nested token header",
  "upstream": [
    "GHSA-8wjv-2p76-3863",
    "CVE-2026-102265"
  ]
}

BREW-MISTRAL-VIBE-CVE-20… (GHSA-8WJV-2P76-3863)

Vulnerability from osv_homebrew – Published: 2026-09-30 10:09 – Updated: 2026-09-30 10:09 – Source website

Summary

PyJWT: Uncaught RecursionError in jwt.decode() on deeply nested token header

Details

Package

pyjwt (PyPI)

Affected versions

tested & verified on: 2.13.0. Every version whose PyJWS._load() translates only ValueError is affected

Description

PyJWS._looad() (jwt/api_jws.py:337) splits the compact token, base64url decodes the header segment and hands it to json.loads() before _verify_signature() runs. The parse is wrapped in except ValueError as e: raise DecodeError(...). That is what makes the documented contract sufficient for untrusted input: except jwt.PyJWTError (or InvalidTokenError) around jwt.decode(token, key, algorithms=[...]).

CPython's JSON decoder raises RecursionError (a RuntimeError subclass, not a ValueError) once nesting crosses the native stack guard. That exception leaves _load(), then jwt.decode(), and matches no PyJWTError handlerr at all. No key and no valid signature are needed: the header is parsed first, so a single unauthenticated request with an unsigned token suffices.

Scope: the recursion threshold is ~65,000 nesting levels; below it the same input yields a clean DecodeError (a 346,800-byte flat header is rejected normally, so depth, not size, is the trigger). A token this large cannot ride in an Authorization header (rejected at HTTP field limits,431 under gunicorn), but body transport (RFC 7662 introspection style) is a standard pattern. Under Flask 3.1.3 / gunicorn 26.2.0 each crafted request returns HTTP 500 instead of 401 and writes a full traceback to the error log; the sync worker survives.

Proof of concept

Against any endpoint that validates a token from its JSON body with the documented pattern:

import base64, json, http.client

def b64url(b): return base64.urlsafe_b64encode(b).rstrip(b"=")

# unsigned token: the header segment is 200,000 nested '[' (266,681 bytes total)
token = (b64url(b"[" * 200_000) + b"." + b64url(b'{"a":1}') + b"." + b64url(b"x")).decode()

conn = http.client.HTTPConnection("127.0.0.1", 8125, timeout=30)
conn.request("POST", "/api/protected", body=json.dumps({"token": token}),
             headers={"Content-Type": "application/json"})
print(conn.getresponse().status)   # 500, expected 401

Determinism: 20/20 crafted requests returned 500 against the reference container (PyJWT 2.13.0, Flask 3.1.3, gunicorn 26.2.0, Python 3.14.7) in 0.12 s (about 6 ms per request in a tight loop, 14 ms for a cold request), each leaving a RecursionError: Stack overflow ... while decoding a JSON array traceback in the error log.

Impact

An unauthenticated attacker can turn every request to a JWT validating endpoint into a server error with a full traceback logged per request, a cheap and repeatable denial of service on the authentication path (no crash, no data exposure).

Fix

Catch RecursionError alongside ValueError in _load() and raise DecodeError, or parse the header with a nonrecursive, depthbounded parser.

Reproduction

A standalone package (docker-compose.yml, Dockerfile, requirements.txt, target app, driver) accompanies this report:

cd <package dir>
docker compose up -d --build
python3 poc_check_then_attack.py
docker compose down -v

poc_pyjwt_recursion.zip

Exit 0= reproduced (control checks green, exactly one crafted request returns 500, traceback verified in docker logs, service alive afterwards); 1 = not reproduced; 2 = checks failed, no attack sent. The package's run_log.txt documents a complete proof run.

Credits

@Nivid42

Maintainer update — 2026-09-09

We reproduced the reported behavior on PyJWT 2.13.0: a deeply nested JSON array in the untrusted compact-JWS header reaches json.loads() before signature verification and raises RecursionError, which is not a PyJWTError. The same input is accepted by the public jwt.decode() path and can escape an application's normal except PyJWTError handling.

The fix is committed as 06573692ebcdec8831c3927513b3e87c31fbbb62. PyJWS._load() now translates both ValueError and RecursionError from header JSON parsing into DecodeError. A regression test covers the deeply nested-header path before signature verification. The full suite passes with 373 tests and 4 intentional cryptography-environment skips.

No release containing the fix has been published yet, so the patched version remains unset pending release planning. The advisory remains medium severity and unpublished.

Maintainer update — 2026-09-11

The verified fix for this advisory is included in PyJWT 2.14.0, released on 2026-09-11 and available on PyPI. PyJWT 2.14.0 is the first release containing the fix. This advisory is now published with 2.14.0 recorded as the patched version.

Severity

5.3 (Medium)


                    
                      CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

References

URL

Type

	https://github.com/jpadilla/pyjwt/security/adviso…	WEB
	https://nvd.nist.gov/vuln/detail/CVE-2026-102265	ADVISORY
	https://github.com/jpadilla/pyjwt/commit/06573692…	WEB
	https://github.com/jpadilla/pyjwt	PACKAGE
	https://github.com/jpadilla/pyjwt/releases/tag/2.14.0	WEB

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": null,
        "range_state": "affected",
        "resource": "pyjwt",
        "resource_purl": "pkg:pypi/pyjwt@2.13.0",
        "upstream_fixed_in": "2.14.0"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "mistral-vibe",
        "purl": "pkg:brew/mistral-vibe"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.17.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/pyjwt@2.13.0",
        "name": "pyjwt",
        "resource": "pyjwt",
        "strategy": "registry",
        "subject_version": "2.13.0"
      }
    ]
  },
  "details": "## Package\n\npyjwt (PyPI)\n\n## Affected versions\n\ntested \u0026 verified on: 2.13.0. Every version whose `PyJWS._load()` translates only `ValueError` is affected\n\n## Description\n\n`PyJWS._looad()` (`jwt/api_jws.py:337`) splits the compact token, base64url decodes the header segment and hands it to `json.loads()` before `_verify_signature()` runs. The parse is wrapped in `except ValueError as e: raise DecodeError(...)`. That is what makes the documented contract sufficient for untrusted input: `except jwt.PyJWTError` (or `InvalidTokenError`) around `jwt.decode(token, key, algorithms=[...])`.\n\nCPython\u0027s JSON decoder raises `RecursionError` (a `RuntimeError` subclass, not a `ValueError`) once nesting crosses the native stack guard. That exception leaves `_load()`, then `jwt.decode()`, and matches no `PyJWTError` handlerr at all. No key and no valid signature are needed: the header is parsed first, so a single unauthenticated request with an unsigned token suffices.\n\nScope: the recursion threshold is ~65,000 nesting levels; below it the same input yields a clean `DecodeError` (a 346,800-byte flat header is rejected normally, so depth, not size, is the trigger). A token this large cannot ride in an `Authorization` header (rejected at HTTP field limits,431 under gunicorn), but body transport (RFC 7662 introspection style) is a standard pattern. Under Flask 3.1.3 / gunicorn 26.2.0 each crafted request returns HTTP 500 instead of 401 and writes a full traceback to the error log; the sync worker survives.\n\n## Proof of concept\n\nAgainst any endpoint that validates a token from its JSON body with the documented pattern:\n\n```python\nimport base64, json, http.client\n\ndef b64url(b): return base64.urlsafe_b64encode(b).rstrip(b\"=\")\n\n# unsigned token: the header segment is 200,000 nested \u0027[\u0027 (266,681 bytes total)\ntoken = (b64url(b\"[\" * 200_000) + b\".\" + b64url(b\u0027{\"a\":1}\u0027) + b\".\" + b64url(b\"x\")).decode()\n\nconn = http.client.HTTPConnection(\"127.0.0.1\", 8125, timeout=30)\nconn.request(\"POST\", \"/api/protected\", body=json.dumps({\"token\": token}),\n             headers={\"Content-Type\": \"application/json\"})\nprint(conn.getresponse().status)   # 500, expected 401\n```\n\nDeterminism: 20/20 crafted requests returned 500 against the reference container (PyJWT 2.13.0, Flask 3.1.3, gunicorn 26.2.0, Python 3.14.7) in 0.12 s (about 6 ms per request in a tight loop, 14 ms for a cold request), each leaving a `RecursionError: Stack overflow ... while decoding a JSON array` traceback in the error log.\n\n## Impact\n\nAn unauthenticated attacker can turn every request to a JWT validating endpoint into a server error with a full traceback logged per request, a cheap and repeatable denial of service on the authentication path (no crash, no data exposure).\n\n## Fix\n\nCatch `RecursionError` alongside `ValueError` in `_load()` and raise `DecodeError`, or parse the header with a nonrecursive, depthbounded parser.\n\n## Reproduction\n\nA standalone package (docker-compose.yml, Dockerfile, requirements.txt, target app, driver) accompanies this report:\n\n```\ncd \u003cpackage dir\u003e\ndocker compose up -d --build\npython3 poc_check_then_attack.py\ndocker compose down -v\n```\n[poc_pyjwt_recursion.zip](https://github.com/user-attachments/files/31614987/poc_pyjwt_recursion.zip)\n\nExit 0= reproduced (control checks green, exactly one crafted request returns 500, traceback verified in `docker logs`, service alive afterwards); 1 = not reproduced; 2 = checks failed, no attack sent. The package\u0027s `run_log.txt` documents a complete proof run.\n\n## Credits\n\n- @Nivid42\n\n## Maintainer update \u2014 2026-09-09\n\nWe reproduced the reported behavior on PyJWT 2.13.0: a deeply nested JSON array in the untrusted compact-JWS header reaches `json.loads()` before signature verification and raises `RecursionError`, which is not a `PyJWTError`. The same input is accepted by the public `jwt.decode()` path and can escape an application\u0027s normal `except PyJWTError` handling.\n\nThe fix is committed as `06573692ebcdec8831c3927513b3e87c31fbbb62`. `PyJWS._load()` now translates both `ValueError` and `RecursionError` from header JSON parsing into `DecodeError`. A regression test covers the deeply nested-header path before signature verification. The full suite passes with 373 tests and 4 intentional cryptography-environment skips.\n\nNo release containing the fix has been published yet, so the patched version remains unset pending release planning. The advisory remains medium severity and unpublished.\n\n## Maintainer update \u2014 2026-09-11\n\nThe verified fix for this advisory is included in PyJWT 2.14.0, released on 2026-09-11 and available on PyPI. PyJWT 2.14.0 is the first release containing the fix. This advisory is now published with 2.14.0 recorded as the patched version.",
  "id": "BREW-mistral-vibe-CVE-2026-102265",
  "modified": "2026-09-30T10:09:38Z",
  "published": "2026-09-30T10:09:38Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/security/advisories/GHSA-8wjv-2p76-3863"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-102265"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/commit/06573692ebcdec8831c3927513b3e87c31fbbb62"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/jpadilla/pyjwt"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/releases/tag/2.14.0"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "PyJWT: Uncaught RecursionError in jwt.decode() on deeply nested token header",
  "upstream": [
    "GHSA-8wjv-2p76-3863",
    "CVE-2026-102265"
  ]
}

BREW-OCI-CLI-CVE-2026-102265 (GHSA-8WJV-2P76-3863)

Vulnerability from osv_homebrew – Published: 2026-09-30 08:58 – Updated: 2026-09-30 08:58 – Source website

Summary

PyJWT: Uncaught RecursionError in jwt.decode() on deeply nested token header

Details

Package

pyjwt (PyPI)

Affected versions

tested & verified on: 2.13.0. Every version whose PyJWS._load() translates only ValueError is affected

Description

PyJWS._looad() (jwt/api_jws.py:337) splits the compact token, base64url decodes the header segment and hands it to json.loads() before _verify_signature() runs. The parse is wrapped in except ValueError as e: raise DecodeError(...). That is what makes the documented contract sufficient for untrusted input: except jwt.PyJWTError (or InvalidTokenError) around jwt.decode(token, key, algorithms=[...]).

CPython's JSON decoder raises RecursionError (a RuntimeError subclass, not a ValueError) once nesting crosses the native stack guard. That exception leaves _load(), then jwt.decode(), and matches no PyJWTError handlerr at all. No key and no valid signature are needed: the header is parsed first, so a single unauthenticated request with an unsigned token suffices.

Scope: the recursion threshold is ~65,000 nesting levels; below it the same input yields a clean DecodeError (a 346,800-byte flat header is rejected normally, so depth, not size, is the trigger). A token this large cannot ride in an Authorization header (rejected at HTTP field limits,431 under gunicorn), but body transport (RFC 7662 introspection style) is a standard pattern. Under Flask 3.1.3 / gunicorn 26.2.0 each crafted request returns HTTP 500 instead of 401 and writes a full traceback to the error log; the sync worker survives.

Proof of concept

Against any endpoint that validates a token from its JSON body with the documented pattern:

import base64, json, http.client

def b64url(b): return base64.urlsafe_b64encode(b).rstrip(b"=")

# unsigned token: the header segment is 200,000 nested '[' (266,681 bytes total)
token = (b64url(b"[" * 200_000) + b"." + b64url(b'{"a":1}') + b"." + b64url(b"x")).decode()

conn = http.client.HTTPConnection("127.0.0.1", 8125, timeout=30)
conn.request("POST", "/api/protected", body=json.dumps({"token": token}),
             headers={"Content-Type": "application/json"})
print(conn.getresponse().status)   # 500, expected 401

Determinism: 20/20 crafted requests returned 500 against the reference container (PyJWT 2.13.0, Flask 3.1.3, gunicorn 26.2.0, Python 3.14.7) in 0.12 s (about 6 ms per request in a tight loop, 14 ms for a cold request), each leaving a RecursionError: Stack overflow ... while decoding a JSON array traceback in the error log.

Impact

An unauthenticated attacker can turn every request to a JWT validating endpoint into a server error with a full traceback logged per request, a cheap and repeatable denial of service on the authentication path (no crash, no data exposure).

Fix

Catch RecursionError alongside ValueError in _load() and raise DecodeError, or parse the header with a nonrecursive, depthbounded parser.

Reproduction

A standalone package (docker-compose.yml, Dockerfile, requirements.txt, target app, driver) accompanies this report:

cd <package dir>
docker compose up -d --build
python3 poc_check_then_attack.py
docker compose down -v

poc_pyjwt_recursion.zip

Exit 0= reproduced (control checks green, exactly one crafted request returns 500, traceback verified in docker logs, service alive afterwards); 1 = not reproduced; 2 = checks failed, no attack sent. The package's run_log.txt documents a complete proof run.

Credits

@Nivid42

Maintainer update — 2026-09-09

We reproduced the reported behavior on PyJWT 2.13.0: a deeply nested JSON array in the untrusted compact-JWS header reaches json.loads() before signature verification and raises RecursionError, which is not a PyJWTError. The same input is accepted by the public jwt.decode() path and can escape an application's normal except PyJWTError handling.

The fix is committed as 06573692ebcdec8831c3927513b3e87c31fbbb62. PyJWS._load() now translates both ValueError and RecursionError from header JSON parsing into DecodeError. A regression test covers the deeply nested-header path before signature verification. The full suite passes with 373 tests and 4 intentional cryptography-environment skips.

No release containing the fix has been published yet, so the patched version remains unset pending release planning. The advisory remains medium severity and unpublished.

Maintainer update — 2026-09-11

The verified fix for this advisory is included in PyJWT 2.14.0, released on 2026-09-11 and available on PyPI. PyJWT 2.14.0 is the first release containing the fix. This advisory is now published with 2.14.0 recorded as the patched version.

Severity

5.3 (Medium)


                    
                      CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

References

URL

Type

	https://github.com/jpadilla/pyjwt/security/adviso…	WEB
	https://nvd.nist.gov/vuln/detail/CVE-2026-102265	ADVISORY
	https://github.com/jpadilla/pyjwt/commit/06573692…	WEB
	https://github.com/jpadilla/pyjwt	PACKAGE
	https://github.com/jpadilla/pyjwt/releases/tag/2.14.0	WEB

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": "bump",
        "range_state": "fixed",
        "resource": "pyjwt",
        "resource_purl": "pkg:pypi/pyjwt@2.14.0",
        "upstream_fixed_in": "2.14.0"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "oci-cli",
        "purl": "pkg:brew/oci-cli"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.89.1"
            },
            {
              "fixed": "3.93.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/pyjwt@2.14.0",
        "name": "pyjwt",
        "resource": "pyjwt",
        "strategy": "registry",
        "subject_version": "2.14.0"
      }
    ]
  },
  "details": "## Package\n\npyjwt (PyPI)\n\n## Affected versions\n\ntested \u0026 verified on: 2.13.0. Every version whose `PyJWS._load()` translates only `ValueError` is affected\n\n## Description\n\n`PyJWS._looad()` (`jwt/api_jws.py:337`) splits the compact token, base64url decodes the header segment and hands it to `json.loads()` before `_verify_signature()` runs. The parse is wrapped in `except ValueError as e: raise DecodeError(...)`. That is what makes the documented contract sufficient for untrusted input: `except jwt.PyJWTError` (or `InvalidTokenError`) around `jwt.decode(token, key, algorithms=[...])`.\n\nCPython\u0027s JSON decoder raises `RecursionError` (a `RuntimeError` subclass, not a `ValueError`) once nesting crosses the native stack guard. That exception leaves `_load()`, then `jwt.decode()`, and matches no `PyJWTError` handlerr at all. No key and no valid signature are needed: the header is parsed first, so a single unauthenticated request with an unsigned token suffices.\n\nScope: the recursion threshold is ~65,000 nesting levels; below it the same input yields a clean `DecodeError` (a 346,800-byte flat header is rejected normally, so depth, not size, is the trigger). A token this large cannot ride in an `Authorization` header (rejected at HTTP field limits,431 under gunicorn), but body transport (RFC 7662 introspection style) is a standard pattern. Under Flask 3.1.3 / gunicorn 26.2.0 each crafted request returns HTTP 500 instead of 401 and writes a full traceback to the error log; the sync worker survives.\n\n## Proof of concept\n\nAgainst any endpoint that validates a token from its JSON body with the documented pattern:\n\n```python\nimport base64, json, http.client\n\ndef b64url(b): return base64.urlsafe_b64encode(b).rstrip(b\"=\")\n\n# unsigned token: the header segment is 200,000 nested \u0027[\u0027 (266,681 bytes total)\ntoken = (b64url(b\"[\" * 200_000) + b\".\" + b64url(b\u0027{\"a\":1}\u0027) + b\".\" + b64url(b\"x\")).decode()\n\nconn = http.client.HTTPConnection(\"127.0.0.1\", 8125, timeout=30)\nconn.request(\"POST\", \"/api/protected\", body=json.dumps({\"token\": token}),\n             headers={\"Content-Type\": \"application/json\"})\nprint(conn.getresponse().status)   # 500, expected 401\n```\n\nDeterminism: 20/20 crafted requests returned 500 against the reference container (PyJWT 2.13.0, Flask 3.1.3, gunicorn 26.2.0, Python 3.14.7) in 0.12 s (about 6 ms per request in a tight loop, 14 ms for a cold request), each leaving a `RecursionError: Stack overflow ... while decoding a JSON array` traceback in the error log.\n\n## Impact\n\nAn unauthenticated attacker can turn every request to a JWT validating endpoint into a server error with a full traceback logged per request, a cheap and repeatable denial of service on the authentication path (no crash, no data exposure).\n\n## Fix\n\nCatch `RecursionError` alongside `ValueError` in `_load()` and raise `DecodeError`, or parse the header with a nonrecursive, depthbounded parser.\n\n## Reproduction\n\nA standalone package (docker-compose.yml, Dockerfile, requirements.txt, target app, driver) accompanies this report:\n\n```\ncd \u003cpackage dir\u003e\ndocker compose up -d --build\npython3 poc_check_then_attack.py\ndocker compose down -v\n```\n[poc_pyjwt_recursion.zip](https://github.com/user-attachments/files/31614987/poc_pyjwt_recursion.zip)\n\nExit 0= reproduced (control checks green, exactly one crafted request returns 500, traceback verified in `docker logs`, service alive afterwards); 1 = not reproduced; 2 = checks failed, no attack sent. The package\u0027s `run_log.txt` documents a complete proof run.\n\n## Credits\n\n- @Nivid42\n\n## Maintainer update \u2014 2026-09-09\n\nWe reproduced the reported behavior on PyJWT 2.13.0: a deeply nested JSON array in the untrusted compact-JWS header reaches `json.loads()` before signature verification and raises `RecursionError`, which is not a `PyJWTError`. The same input is accepted by the public `jwt.decode()` path and can escape an application\u0027s normal `except PyJWTError` handling.\n\nThe fix is committed as `06573692ebcdec8831c3927513b3e87c31fbbb62`. `PyJWS._load()` now translates both `ValueError` and `RecursionError` from header JSON parsing into `DecodeError`. A regression test covers the deeply nested-header path before signature verification. The full suite passes with 373 tests and 4 intentional cryptography-environment skips.\n\nNo release containing the fix has been published yet, so the patched version remains unset pending release planning. The advisory remains medium severity and unpublished.\n\n## Maintainer update \u2014 2026-09-11\n\nThe verified fix for this advisory is included in PyJWT 2.14.0, released on 2026-09-11 and available on PyPI. PyJWT 2.14.0 is the first release containing the fix. This advisory is now published with 2.14.0 recorded as the patched version.",
  "id": "BREW-oci-cli-CVE-2026-102265",
  "modified": "2026-09-30T08:58:35Z",
  "published": "2026-09-30T08:58:35Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/security/advisories/GHSA-8wjv-2p76-3863"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-102265"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/commit/06573692ebcdec8831c3927513b3e87c31fbbb62"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/jpadilla/pyjwt"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/releases/tag/2.14.0"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "PyJWT: Uncaught RecursionError in jwt.decode() on deeply nested token header",
  "upstream": [
    "GHSA-8wjv-2p76-3863",
    "CVE-2026-102265"
  ]
}

BREW-OTERM-CVE-2026-102265 (GHSA-8WJV-2P76-3863)

Vulnerability from osv_homebrew – Published: 2026-09-30 09:35 – Updated: 2026-09-30 09:35 – Source website

Summary

PyJWT: Uncaught RecursionError in jwt.decode() on deeply nested token header

Details

Package

pyjwt (PyPI)

Affected versions

tested & verified on: 2.13.0. Every version whose PyJWS._load() translates only ValueError is affected

Description

PyJWS._looad() (jwt/api_jws.py:337) splits the compact token, base64url decodes the header segment and hands it to json.loads() before _verify_signature() runs. The parse is wrapped in except ValueError as e: raise DecodeError(...). That is what makes the documented contract sufficient for untrusted input: except jwt.PyJWTError (or InvalidTokenError) around jwt.decode(token, key, algorithms=[...]).

CPython's JSON decoder raises RecursionError (a RuntimeError subclass, not a ValueError) once nesting crosses the native stack guard. That exception leaves _load(), then jwt.decode(), and matches no PyJWTError handlerr at all. No key and no valid signature are needed: the header is parsed first, so a single unauthenticated request with an unsigned token suffices.

Scope: the recursion threshold is ~65,000 nesting levels; below it the same input yields a clean DecodeError (a 346,800-byte flat header is rejected normally, so depth, not size, is the trigger). A token this large cannot ride in an Authorization header (rejected at HTTP field limits,431 under gunicorn), but body transport (RFC 7662 introspection style) is a standard pattern. Under Flask 3.1.3 / gunicorn 26.2.0 each crafted request returns HTTP 500 instead of 401 and writes a full traceback to the error log; the sync worker survives.

Proof of concept

Against any endpoint that validates a token from its JSON body with the documented pattern:

import base64, json, http.client

def b64url(b): return base64.urlsafe_b64encode(b).rstrip(b"=")

# unsigned token: the header segment is 200,000 nested '[' (266,681 bytes total)
token = (b64url(b"[" * 200_000) + b"." + b64url(b'{"a":1}') + b"." + b64url(b"x")).decode()

conn = http.client.HTTPConnection("127.0.0.1", 8125, timeout=30)
conn.request("POST", "/api/protected", body=json.dumps({"token": token}),
             headers={"Content-Type": "application/json"})
print(conn.getresponse().status)   # 500, expected 401

Determinism: 20/20 crafted requests returned 500 against the reference container (PyJWT 2.13.0, Flask 3.1.3, gunicorn 26.2.0, Python 3.14.7) in 0.12 s (about 6 ms per request in a tight loop, 14 ms for a cold request), each leaving a RecursionError: Stack overflow ... while decoding a JSON array traceback in the error log.

Impact

An unauthenticated attacker can turn every request to a JWT validating endpoint into a server error with a full traceback logged per request, a cheap and repeatable denial of service on the authentication path (no crash, no data exposure).

Fix

Catch RecursionError alongside ValueError in _load() and raise DecodeError, or parse the header with a nonrecursive, depthbounded parser.

Reproduction

A standalone package (docker-compose.yml, Dockerfile, requirements.txt, target app, driver) accompanies this report:

cd <package dir>
docker compose up -d --build
python3 poc_check_then_attack.py
docker compose down -v

poc_pyjwt_recursion.zip

Exit 0= reproduced (control checks green, exactly one crafted request returns 500, traceback verified in docker logs, service alive afterwards); 1 = not reproduced; 2 = checks failed, no attack sent. The package's run_log.txt documents a complete proof run.

Credits

@Nivid42

Maintainer update — 2026-09-09

We reproduced the reported behavior on PyJWT 2.13.0: a deeply nested JSON array in the untrusted compact-JWS header reaches json.loads() before signature verification and raises RecursionError, which is not a PyJWTError. The same input is accepted by the public jwt.decode() path and can escape an application's normal except PyJWTError handling.

The fix is committed as 06573692ebcdec8831c3927513b3e87c31fbbb62. PyJWS._load() now translates both ValueError and RecursionError from header JSON parsing into DecodeError. A regression test covers the deeply nested-header path before signature verification. The full suite passes with 373 tests and 4 intentional cryptography-environment skips.

No release containing the fix has been published yet, so the patched version remains unset pending release planning. The advisory remains medium severity and unpublished.

Maintainer update — 2026-09-11

The verified fix for this advisory is included in PyJWT 2.14.0, released on 2026-09-11 and available on PyPI. PyJWT 2.14.0 is the first release containing the fix. This advisory is now published with 2.14.0 recorded as the patched version.

Severity

5.3 (Medium)


                    
                      CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

References

URL

Type

	https://github.com/jpadilla/pyjwt/security/adviso…	WEB
	https://nvd.nist.gov/vuln/detail/CVE-2026-102265	ADVISORY
	https://github.com/jpadilla/pyjwt/commit/06573692…	WEB
	https://github.com/jpadilla/pyjwt	PACKAGE
	https://github.com/jpadilla/pyjwt/releases/tag/2.14.0	WEB

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": "bump",
        "range_state": "fixed",
        "resource": "pyjwt",
        "resource_purl": "pkg:pypi/pyjwt@2.15.0",
        "upstream_fixed_in": "2.14.0"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "oterm",
        "purl": "pkg:brew/oterm"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.17.2_1"
            },
            {
              "fixed": "0.25.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/pyjwt@2.15.0",
        "name": "pyjwt",
        "resource": "pyjwt",
        "strategy": "registry",
        "subject_version": "2.15.0"
      }
    ]
  },
  "details": "## Package\n\npyjwt (PyPI)\n\n## Affected versions\n\ntested \u0026 verified on: 2.13.0. Every version whose `PyJWS._load()` translates only `ValueError` is affected\n\n## Description\n\n`PyJWS._looad()` (`jwt/api_jws.py:337`) splits the compact token, base64url decodes the header segment and hands it to `json.loads()` before `_verify_signature()` runs. The parse is wrapped in `except ValueError as e: raise DecodeError(...)`. That is what makes the documented contract sufficient for untrusted input: `except jwt.PyJWTError` (or `InvalidTokenError`) around `jwt.decode(token, key, algorithms=[...])`.\n\nCPython\u0027s JSON decoder raises `RecursionError` (a `RuntimeError` subclass, not a `ValueError`) once nesting crosses the native stack guard. That exception leaves `_load()`, then `jwt.decode()`, and matches no `PyJWTError` handlerr at all. No key and no valid signature are needed: the header is parsed first, so a single unauthenticated request with an unsigned token suffices.\n\nScope: the recursion threshold is ~65,000 nesting levels; below it the same input yields a clean `DecodeError` (a 346,800-byte flat header is rejected normally, so depth, not size, is the trigger). A token this large cannot ride in an `Authorization` header (rejected at HTTP field limits,431 under gunicorn), but body transport (RFC 7662 introspection style) is a standard pattern. Under Flask 3.1.3 / gunicorn 26.2.0 each crafted request returns HTTP 500 instead of 401 and writes a full traceback to the error log; the sync worker survives.\n\n## Proof of concept\n\nAgainst any endpoint that validates a token from its JSON body with the documented pattern:\n\n```python\nimport base64, json, http.client\n\ndef b64url(b): return base64.urlsafe_b64encode(b).rstrip(b\"=\")\n\n# unsigned token: the header segment is 200,000 nested \u0027[\u0027 (266,681 bytes total)\ntoken = (b64url(b\"[\" * 200_000) + b\".\" + b64url(b\u0027{\"a\":1}\u0027) + b\".\" + b64url(b\"x\")).decode()\n\nconn = http.client.HTTPConnection(\"127.0.0.1\", 8125, timeout=30)\nconn.request(\"POST\", \"/api/protected\", body=json.dumps({\"token\": token}),\n             headers={\"Content-Type\": \"application/json\"})\nprint(conn.getresponse().status)   # 500, expected 401\n```\n\nDeterminism: 20/20 crafted requests returned 500 against the reference container (PyJWT 2.13.0, Flask 3.1.3, gunicorn 26.2.0, Python 3.14.7) in 0.12 s (about 6 ms per request in a tight loop, 14 ms for a cold request), each leaving a `RecursionError: Stack overflow ... while decoding a JSON array` traceback in the error log.\n\n## Impact\n\nAn unauthenticated attacker can turn every request to a JWT validating endpoint into a server error with a full traceback logged per request, a cheap and repeatable denial of service on the authentication path (no crash, no data exposure).\n\n## Fix\n\nCatch `RecursionError` alongside `ValueError` in `_load()` and raise `DecodeError`, or parse the header with a nonrecursive, depthbounded parser.\n\n## Reproduction\n\nA standalone package (docker-compose.yml, Dockerfile, requirements.txt, target app, driver) accompanies this report:\n\n```\ncd \u003cpackage dir\u003e\ndocker compose up -d --build\npython3 poc_check_then_attack.py\ndocker compose down -v\n```\n[poc_pyjwt_recursion.zip](https://github.com/user-attachments/files/31614987/poc_pyjwt_recursion.zip)\n\nExit 0= reproduced (control checks green, exactly one crafted request returns 500, traceback verified in `docker logs`, service alive afterwards); 1 = not reproduced; 2 = checks failed, no attack sent. The package\u0027s `run_log.txt` documents a complete proof run.\n\n## Credits\n\n- @Nivid42\n\n## Maintainer update \u2014 2026-09-09\n\nWe reproduced the reported behavior on PyJWT 2.13.0: a deeply nested JSON array in the untrusted compact-JWS header reaches `json.loads()` before signature verification and raises `RecursionError`, which is not a `PyJWTError`. The same input is accepted by the public `jwt.decode()` path and can escape an application\u0027s normal `except PyJWTError` handling.\n\nThe fix is committed as `06573692ebcdec8831c3927513b3e87c31fbbb62`. `PyJWS._load()` now translates both `ValueError` and `RecursionError` from header JSON parsing into `DecodeError`. A regression test covers the deeply nested-header path before signature verification. The full suite passes with 373 tests and 4 intentional cryptography-environment skips.\n\nNo release containing the fix has been published yet, so the patched version remains unset pending release planning. The advisory remains medium severity and unpublished.\n\n## Maintainer update \u2014 2026-09-11\n\nThe verified fix for this advisory is included in PyJWT 2.14.0, released on 2026-09-11 and available on PyPI. PyJWT 2.14.0 is the first release containing the fix. This advisory is now published with 2.14.0 recorded as the patched version.",
  "id": "BREW-oterm-CVE-2026-102265",
  "modified": "2026-09-30T09:35:20Z",
  "published": "2026-09-30T09:35:20Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/security/advisories/GHSA-8wjv-2p76-3863"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-102265"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/commit/06573692ebcdec8831c3927513b3e87c31fbbb62"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/jpadilla/pyjwt"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/releases/tag/2.14.0"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "PyJWT: Uncaught RecursionError in jwt.decode() on deeply nested token header",
  "upstream": [
    "GHSA-8wjv-2p76-3863",
    "CVE-2026-102265"
  ]
}

BREW-RAPID-MLX-CVE-2026-102265 (GHSA-8WJV-2P76-3863)

Vulnerability from osv_homebrew – Published: 2026-09-30 10:08 – Updated: 2026-09-30 10:08 – Source website

Summary

PyJWT: Uncaught RecursionError in jwt.decode() on deeply nested token header

Details

Package

pyjwt (PyPI)

Affected versions

tested & verified on: 2.13.0. Every version whose PyJWS._load() translates only ValueError is affected

Description

PyJWS._looad() (jwt/api_jws.py:337) splits the compact token, base64url decodes the header segment and hands it to json.loads() before _verify_signature() runs. The parse is wrapped in except ValueError as e: raise DecodeError(...). That is what makes the documented contract sufficient for untrusted input: except jwt.PyJWTError (or InvalidTokenError) around jwt.decode(token, key, algorithms=[...]).

CPython's JSON decoder raises RecursionError (a RuntimeError subclass, not a ValueError) once nesting crosses the native stack guard. That exception leaves _load(), then jwt.decode(), and matches no PyJWTError handlerr at all. No key and no valid signature are needed: the header is parsed first, so a single unauthenticated request with an unsigned token suffices.

Scope: the recursion threshold is ~65,000 nesting levels; below it the same input yields a clean DecodeError (a 346,800-byte flat header is rejected normally, so depth, not size, is the trigger). A token this large cannot ride in an Authorization header (rejected at HTTP field limits,431 under gunicorn), but body transport (RFC 7662 introspection style) is a standard pattern. Under Flask 3.1.3 / gunicorn 26.2.0 each crafted request returns HTTP 500 instead of 401 and writes a full traceback to the error log; the sync worker survives.

Proof of concept

Against any endpoint that validates a token from its JSON body with the documented pattern:

import base64, json, http.client

def b64url(b): return base64.urlsafe_b64encode(b).rstrip(b"=")

# unsigned token: the header segment is 200,000 nested '[' (266,681 bytes total)
token = (b64url(b"[" * 200_000) + b"." + b64url(b'{"a":1}') + b"." + b64url(b"x")).decode()

conn = http.client.HTTPConnection("127.0.0.1", 8125, timeout=30)
conn.request("POST", "/api/protected", body=json.dumps({"token": token}),
             headers={"Content-Type": "application/json"})
print(conn.getresponse().status)   # 500, expected 401

Determinism: 20/20 crafted requests returned 500 against the reference container (PyJWT 2.13.0, Flask 3.1.3, gunicorn 26.2.0, Python 3.14.7) in 0.12 s (about 6 ms per request in a tight loop, 14 ms for a cold request), each leaving a RecursionError: Stack overflow ... while decoding a JSON array traceback in the error log.

Impact

An unauthenticated attacker can turn every request to a JWT validating endpoint into a server error with a full traceback logged per request, a cheap and repeatable denial of service on the authentication path (no crash, no data exposure).

Fix

Catch RecursionError alongside ValueError in _load() and raise DecodeError, or parse the header with a nonrecursive, depthbounded parser.

Reproduction

A standalone package (docker-compose.yml, Dockerfile, requirements.txt, target app, driver) accompanies this report:

cd <package dir>
docker compose up -d --build
python3 poc_check_then_attack.py
docker compose down -v

poc_pyjwt_recursion.zip

Exit 0= reproduced (control checks green, exactly one crafted request returns 500, traceback verified in docker logs, service alive afterwards); 1 = not reproduced; 2 = checks failed, no attack sent. The package's run_log.txt documents a complete proof run.

Credits

@Nivid42

Maintainer update — 2026-09-09

We reproduced the reported behavior on PyJWT 2.13.0: a deeply nested JSON array in the untrusted compact-JWS header reaches json.loads() before signature verification and raises RecursionError, which is not a PyJWTError. The same input is accepted by the public jwt.decode() path and can escape an application's normal except PyJWTError handling.

The fix is committed as 06573692ebcdec8831c3927513b3e87c31fbbb62. PyJWS._load() now translates both ValueError and RecursionError from header JSON parsing into DecodeError. A regression test covers the deeply nested-header path before signature verification. The full suite passes with 373 tests and 4 intentional cryptography-environment skips.

No release containing the fix has been published yet, so the patched version remains unset pending release planning. The advisory remains medium severity and unpublished.

Maintainer update — 2026-09-11

The verified fix for this advisory is included in PyJWT 2.14.0, released on 2026-09-11 and available on PyPI. PyJWT 2.14.0 is the first release containing the fix. This advisory is now published with 2.14.0 recorded as the patched version.

Severity

5.3 (Medium)


                    
                      CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

References

URL

Type

	https://github.com/jpadilla/pyjwt/security/adviso…	WEB
	https://nvd.nist.gov/vuln/detail/CVE-2026-102265	ADVISORY
	https://github.com/jpadilla/pyjwt/commit/06573692…	WEB
	https://github.com/jpadilla/pyjwt	PACKAGE
	https://github.com/jpadilla/pyjwt/releases/tag/2.14.0	WEB

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": "bump",
        "range_state": "fixed",
        "resource": "pyjwt",
        "resource_purl": "pkg:pypi/pyjwt@2.15.0",
        "upstream_fixed_in": "2.14.0"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "rapid-mlx",
        "purl": "pkg:brew/rapid-mlx"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.10.12"
            },
            {
              "fixed": "0.14.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/pyjwt@2.15.0",
        "name": "pyjwt",
        "resource": "pyjwt",
        "strategy": "registry",
        "subject_version": "2.15.0"
      }
    ]
  },
  "details": "## Package\n\npyjwt (PyPI)\n\n## Affected versions\n\ntested \u0026 verified on: 2.13.0. Every version whose `PyJWS._load()` translates only `ValueError` is affected\n\n## Description\n\n`PyJWS._looad()` (`jwt/api_jws.py:337`) splits the compact token, base64url decodes the header segment and hands it to `json.loads()` before `_verify_signature()` runs. The parse is wrapped in `except ValueError as e: raise DecodeError(...)`. That is what makes the documented contract sufficient for untrusted input: `except jwt.PyJWTError` (or `InvalidTokenError`) around `jwt.decode(token, key, algorithms=[...])`.\n\nCPython\u0027s JSON decoder raises `RecursionError` (a `RuntimeError` subclass, not a `ValueError`) once nesting crosses the native stack guard. That exception leaves `_load()`, then `jwt.decode()`, and matches no `PyJWTError` handlerr at all. No key and no valid signature are needed: the header is parsed first, so a single unauthenticated request with an unsigned token suffices.\n\nScope: the recursion threshold is ~65,000 nesting levels; below it the same input yields a clean `DecodeError` (a 346,800-byte flat header is rejected normally, so depth, not size, is the trigger). A token this large cannot ride in an `Authorization` header (rejected at HTTP field limits,431 under gunicorn), but body transport (RFC 7662 introspection style) is a standard pattern. Under Flask 3.1.3 / gunicorn 26.2.0 each crafted request returns HTTP 500 instead of 401 and writes a full traceback to the error log; the sync worker survives.\n\n## Proof of concept\n\nAgainst any endpoint that validates a token from its JSON body with the documented pattern:\n\n```python\nimport base64, json, http.client\n\ndef b64url(b): return base64.urlsafe_b64encode(b).rstrip(b\"=\")\n\n# unsigned token: the header segment is 200,000 nested \u0027[\u0027 (266,681 bytes total)\ntoken = (b64url(b\"[\" * 200_000) + b\".\" + b64url(b\u0027{\"a\":1}\u0027) + b\".\" + b64url(b\"x\")).decode()\n\nconn = http.client.HTTPConnection(\"127.0.0.1\", 8125, timeout=30)\nconn.request(\"POST\", \"/api/protected\", body=json.dumps({\"token\": token}),\n             headers={\"Content-Type\": \"application/json\"})\nprint(conn.getresponse().status)   # 500, expected 401\n```\n\nDeterminism: 20/20 crafted requests returned 500 against the reference container (PyJWT 2.13.0, Flask 3.1.3, gunicorn 26.2.0, Python 3.14.7) in 0.12 s (about 6 ms per request in a tight loop, 14 ms for a cold request), each leaving a `RecursionError: Stack overflow ... while decoding a JSON array` traceback in the error log.\n\n## Impact\n\nAn unauthenticated attacker can turn every request to a JWT validating endpoint into a server error with a full traceback logged per request, a cheap and repeatable denial of service on the authentication path (no crash, no data exposure).\n\n## Fix\n\nCatch `RecursionError` alongside `ValueError` in `_load()` and raise `DecodeError`, or parse the header with a nonrecursive, depthbounded parser.\n\n## Reproduction\n\nA standalone package (docker-compose.yml, Dockerfile, requirements.txt, target app, driver) accompanies this report:\n\n```\ncd \u003cpackage dir\u003e\ndocker compose up -d --build\npython3 poc_check_then_attack.py\ndocker compose down -v\n```\n[poc_pyjwt_recursion.zip](https://github.com/user-attachments/files/31614987/poc_pyjwt_recursion.zip)\n\nExit 0= reproduced (control checks green, exactly one crafted request returns 500, traceback verified in `docker logs`, service alive afterwards); 1 = not reproduced; 2 = checks failed, no attack sent. The package\u0027s `run_log.txt` documents a complete proof run.\n\n## Credits\n\n- @Nivid42\n\n## Maintainer update \u2014 2026-09-09\n\nWe reproduced the reported behavior on PyJWT 2.13.0: a deeply nested JSON array in the untrusted compact-JWS header reaches `json.loads()` before signature verification and raises `RecursionError`, which is not a `PyJWTError`. The same input is accepted by the public `jwt.decode()` path and can escape an application\u0027s normal `except PyJWTError` handling.\n\nThe fix is committed as `06573692ebcdec8831c3927513b3e87c31fbbb62`. `PyJWS._load()` now translates both `ValueError` and `RecursionError` from header JSON parsing into `DecodeError`. A regression test covers the deeply nested-header path before signature verification. The full suite passes with 373 tests and 4 intentional cryptography-environment skips.\n\nNo release containing the fix has been published yet, so the patched version remains unset pending release planning. The advisory remains medium severity and unpublished.\n\n## Maintainer update \u2014 2026-09-11\n\nThe verified fix for this advisory is included in PyJWT 2.14.0, released on 2026-09-11 and available on PyPI. PyJWT 2.14.0 is the first release containing the fix. This advisory is now published with 2.14.0 recorded as the patched version.",
  "id": "BREW-rapid-mlx-CVE-2026-102265",
  "modified": "2026-09-30T10:08:51Z",
  "published": "2026-09-30T10:08:51Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/security/advisories/GHSA-8wjv-2p76-3863"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-102265"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/commit/06573692ebcdec8831c3927513b3e87c31fbbb62"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/jpadilla/pyjwt"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/releases/tag/2.14.0"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "PyJWT: Uncaught RecursionError in jwt.decode() on deeply nested token header",
  "upstream": [
    "GHSA-8wjv-2p76-3863",
    "CVE-2026-102265"
  ]
}

BREW-SIGSTORE-CVE-2026-102265 (GHSA-8WJV-2P76-3863)

Vulnerability from osv_homebrew – Published: 2026-09-30 09:42 – Updated: 2026-09-30 09:42 – Source website

Summary

PyJWT: Uncaught RecursionError in jwt.decode() on deeply nested token header

Details

Package

pyjwt (PyPI)

Affected versions

tested & verified on: 2.13.0. Every version whose PyJWS._load() translates only ValueError is affected

Description

PyJWS._looad() (jwt/api_jws.py:337) splits the compact token, base64url decodes the header segment and hands it to json.loads() before _verify_signature() runs. The parse is wrapped in except ValueError as e: raise DecodeError(...). That is what makes the documented contract sufficient for untrusted input: except jwt.PyJWTError (or InvalidTokenError) around jwt.decode(token, key, algorithms=[...]).

CPython's JSON decoder raises RecursionError (a RuntimeError subclass, not a ValueError) once nesting crosses the native stack guard. That exception leaves _load(), then jwt.decode(), and matches no PyJWTError handlerr at all. No key and no valid signature are needed: the header is parsed first, so a single unauthenticated request with an unsigned token suffices.

Scope: the recursion threshold is ~65,000 nesting levels; below it the same input yields a clean DecodeError (a 346,800-byte flat header is rejected normally, so depth, not size, is the trigger). A token this large cannot ride in an Authorization header (rejected at HTTP field limits,431 under gunicorn), but body transport (RFC 7662 introspection style) is a standard pattern. Under Flask 3.1.3 / gunicorn 26.2.0 each crafted request returns HTTP 500 instead of 401 and writes a full traceback to the error log; the sync worker survives.

Proof of concept

Against any endpoint that validates a token from its JSON body with the documented pattern:

import base64, json, http.client

def b64url(b): return base64.urlsafe_b64encode(b).rstrip(b"=")

# unsigned token: the header segment is 200,000 nested '[' (266,681 bytes total)
token = (b64url(b"[" * 200_000) + b"." + b64url(b'{"a":1}') + b"." + b64url(b"x")).decode()

conn = http.client.HTTPConnection("127.0.0.1", 8125, timeout=30)
conn.request("POST", "/api/protected", body=json.dumps({"token": token}),
             headers={"Content-Type": "application/json"})
print(conn.getresponse().status)   # 500, expected 401

Determinism: 20/20 crafted requests returned 500 against the reference container (PyJWT 2.13.0, Flask 3.1.3, gunicorn 26.2.0, Python 3.14.7) in 0.12 s (about 6 ms per request in a tight loop, 14 ms for a cold request), each leaving a RecursionError: Stack overflow ... while decoding a JSON array traceback in the error log.

Impact

An unauthenticated attacker can turn every request to a JWT validating endpoint into a server error with a full traceback logged per request, a cheap and repeatable denial of service on the authentication path (no crash, no data exposure).

Fix

Catch RecursionError alongside ValueError in _load() and raise DecodeError, or parse the header with a nonrecursive, depthbounded parser.

Reproduction

A standalone package (docker-compose.yml, Dockerfile, requirements.txt, target app, driver) accompanies this report:

cd <package dir>
docker compose up -d --build
python3 poc_check_then_attack.py
docker compose down -v

poc_pyjwt_recursion.zip

Exit 0= reproduced (control checks green, exactly one crafted request returns 500, traceback verified in docker logs, service alive afterwards); 1 = not reproduced; 2 = checks failed, no attack sent. The package's run_log.txt documents a complete proof run.

Credits

@Nivid42

Maintainer update — 2026-09-09

We reproduced the reported behavior on PyJWT 2.13.0: a deeply nested JSON array in the untrusted compact-JWS header reaches json.loads() before signature verification and raises RecursionError, which is not a PyJWTError. The same input is accepted by the public jwt.decode() path and can escape an application's normal except PyJWTError handling.

The fix is committed as 06573692ebcdec8831c3927513b3e87c31fbbb62. PyJWS._load() now translates both ValueError and RecursionError from header JSON parsing into DecodeError. A regression test covers the deeply nested-header path before signature verification. The full suite passes with 373 tests and 4 intentional cryptography-environment skips.

No release containing the fix has been published yet, so the patched version remains unset pending release planning. The advisory remains medium severity and unpublished.

Maintainer update — 2026-09-11

The verified fix for this advisory is included in PyJWT 2.14.0, released on 2026-09-11 and available on PyPI. PyJWT 2.14.0 is the first release containing the fix. This advisory is now published with 2.14.0 recorded as the patched version.

Severity

5.3 (Medium)


                    
                      CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

References

URL

Type

	https://github.com/jpadilla/pyjwt/security/adviso…	WEB
	https://nvd.nist.gov/vuln/detail/CVE-2026-102265	ADVISORY
	https://github.com/jpadilla/pyjwt/commit/06573692…	WEB
	https://github.com/jpadilla/pyjwt	PACKAGE
	https://github.com/jpadilla/pyjwt/releases/tag/2.14.0	WEB

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": null,
        "range_state": "affected",
        "resource": "pyjwt",
        "resource_purl": "pkg:pypi/pyjwt@2.13.0",
        "upstream_fixed_in": "2.14.0"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "sigstore",
        "purl": "pkg:brew/sigstore"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.2.0_8"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/pyjwt@2.13.0",
        "name": "pyjwt",
        "resource": "pyjwt",
        "strategy": "registry",
        "subject_version": "2.13.0"
      }
    ]
  },
  "details": "## Package\n\npyjwt (PyPI)\n\n## Affected versions\n\ntested \u0026 verified on: 2.13.0. Every version whose `PyJWS._load()` translates only `ValueError` is affected\n\n## Description\n\n`PyJWS._looad()` (`jwt/api_jws.py:337`) splits the compact token, base64url decodes the header segment and hands it to `json.loads()` before `_verify_signature()` runs. The parse is wrapped in `except ValueError as e: raise DecodeError(...)`. That is what makes the documented contract sufficient for untrusted input: `except jwt.PyJWTError` (or `InvalidTokenError`) around `jwt.decode(token, key, algorithms=[...])`.\n\nCPython\u0027s JSON decoder raises `RecursionError` (a `RuntimeError` subclass, not a `ValueError`) once nesting crosses the native stack guard. That exception leaves `_load()`, then `jwt.decode()`, and matches no `PyJWTError` handlerr at all. No key and no valid signature are needed: the header is parsed first, so a single unauthenticated request with an unsigned token suffices.\n\nScope: the recursion threshold is ~65,000 nesting levels; below it the same input yields a clean `DecodeError` (a 346,800-byte flat header is rejected normally, so depth, not size, is the trigger). A token this large cannot ride in an `Authorization` header (rejected at HTTP field limits,431 under gunicorn), but body transport (RFC 7662 introspection style) is a standard pattern. Under Flask 3.1.3 / gunicorn 26.2.0 each crafted request returns HTTP 500 instead of 401 and writes a full traceback to the error log; the sync worker survives.\n\n## Proof of concept\n\nAgainst any endpoint that validates a token from its JSON body with the documented pattern:\n\n```python\nimport base64, json, http.client\n\ndef b64url(b): return base64.urlsafe_b64encode(b).rstrip(b\"=\")\n\n# unsigned token: the header segment is 200,000 nested \u0027[\u0027 (266,681 bytes total)\ntoken = (b64url(b\"[\" * 200_000) + b\".\" + b64url(b\u0027{\"a\":1}\u0027) + b\".\" + b64url(b\"x\")).decode()\n\nconn = http.client.HTTPConnection(\"127.0.0.1\", 8125, timeout=30)\nconn.request(\"POST\", \"/api/protected\", body=json.dumps({\"token\": token}),\n             headers={\"Content-Type\": \"application/json\"})\nprint(conn.getresponse().status)   # 500, expected 401\n```\n\nDeterminism: 20/20 crafted requests returned 500 against the reference container (PyJWT 2.13.0, Flask 3.1.3, gunicorn 26.2.0, Python 3.14.7) in 0.12 s (about 6 ms per request in a tight loop, 14 ms for a cold request), each leaving a `RecursionError: Stack overflow ... while decoding a JSON array` traceback in the error log.\n\n## Impact\n\nAn unauthenticated attacker can turn every request to a JWT validating endpoint into a server error with a full traceback logged per request, a cheap and repeatable denial of service on the authentication path (no crash, no data exposure).\n\n## Fix\n\nCatch `RecursionError` alongside `ValueError` in `_load()` and raise `DecodeError`, or parse the header with a nonrecursive, depthbounded parser.\n\n## Reproduction\n\nA standalone package (docker-compose.yml, Dockerfile, requirements.txt, target app, driver) accompanies this report:\n\n```\ncd \u003cpackage dir\u003e\ndocker compose up -d --build\npython3 poc_check_then_attack.py\ndocker compose down -v\n```\n[poc_pyjwt_recursion.zip](https://github.com/user-attachments/files/31614987/poc_pyjwt_recursion.zip)\n\nExit 0= reproduced (control checks green, exactly one crafted request returns 500, traceback verified in `docker logs`, service alive afterwards); 1 = not reproduced; 2 = checks failed, no attack sent. The package\u0027s `run_log.txt` documents a complete proof run.\n\n## Credits\n\n- @Nivid42\n\n## Maintainer update \u2014 2026-09-09\n\nWe reproduced the reported behavior on PyJWT 2.13.0: a deeply nested JSON array in the untrusted compact-JWS header reaches `json.loads()` before signature verification and raises `RecursionError`, which is not a `PyJWTError`. The same input is accepted by the public `jwt.decode()` path and can escape an application\u0027s normal `except PyJWTError` handling.\n\nThe fix is committed as `06573692ebcdec8831c3927513b3e87c31fbbb62`. `PyJWS._load()` now translates both `ValueError` and `RecursionError` from header JSON parsing into `DecodeError`. A regression test covers the deeply nested-header path before signature verification. The full suite passes with 373 tests and 4 intentional cryptography-environment skips.\n\nNo release containing the fix has been published yet, so the patched version remains unset pending release planning. The advisory remains medium severity and unpublished.\n\n## Maintainer update \u2014 2026-09-11\n\nThe verified fix for this advisory is included in PyJWT 2.14.0, released on 2026-09-11 and available on PyPI. PyJWT 2.14.0 is the first release containing the fix. This advisory is now published with 2.14.0 recorded as the patched version.",
  "id": "BREW-sigstore-CVE-2026-102265",
  "modified": "2026-09-30T09:42:17Z",
  "published": "2026-09-30T09:42:17Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/security/advisories/GHSA-8wjv-2p76-3863"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-102265"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/commit/06573692ebcdec8831c3927513b3e87c31fbbb62"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/jpadilla/pyjwt"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/releases/tag/2.14.0"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "PyJWT: Uncaught RecursionError in jwt.decode() on deeply nested token header",
  "upstream": [
    "GHSA-8wjv-2p76-3863",
    "CVE-2026-102265"
  ]
}

BREW-SNOWFLAKE-CLI-CVE-2… (GHSA-8WJV-2P76-3863)

Vulnerability from osv_homebrew – Published: 2026-09-30 09:56 – Updated: 2026-09-30 09:56 – Source website

Summary

PyJWT: Uncaught RecursionError in jwt.decode() on deeply nested token header

Details

Package

pyjwt (PyPI)

Affected versions

tested & verified on: 2.13.0. Every version whose PyJWS._load() translates only ValueError is affected

Description

PyJWS._looad() (jwt/api_jws.py:337) splits the compact token, base64url decodes the header segment and hands it to json.loads() before _verify_signature() runs. The parse is wrapped in except ValueError as e: raise DecodeError(...). That is what makes the documented contract sufficient for untrusted input: except jwt.PyJWTError (or InvalidTokenError) around jwt.decode(token, key, algorithms=[...]).

CPython's JSON decoder raises RecursionError (a RuntimeError subclass, not a ValueError) once nesting crosses the native stack guard. That exception leaves _load(), then jwt.decode(), and matches no PyJWTError handlerr at all. No key and no valid signature are needed: the header is parsed first, so a single unauthenticated request with an unsigned token suffices.

Scope: the recursion threshold is ~65,000 nesting levels; below it the same input yields a clean DecodeError (a 346,800-byte flat header is rejected normally, so depth, not size, is the trigger). A token this large cannot ride in an Authorization header (rejected at HTTP field limits,431 under gunicorn), but body transport (RFC 7662 introspection style) is a standard pattern. Under Flask 3.1.3 / gunicorn 26.2.0 each crafted request returns HTTP 500 instead of 401 and writes a full traceback to the error log; the sync worker survives.

Proof of concept

Against any endpoint that validates a token from its JSON body with the documented pattern:

import base64, json, http.client

def b64url(b): return base64.urlsafe_b64encode(b).rstrip(b"=")

# unsigned token: the header segment is 200,000 nested '[' (266,681 bytes total)
token = (b64url(b"[" * 200_000) + b"." + b64url(b'{"a":1}') + b"." + b64url(b"x")).decode()

conn = http.client.HTTPConnection("127.0.0.1", 8125, timeout=30)
conn.request("POST", "/api/protected", body=json.dumps({"token": token}),
             headers={"Content-Type": "application/json"})
print(conn.getresponse().status)   # 500, expected 401

Determinism: 20/20 crafted requests returned 500 against the reference container (PyJWT 2.13.0, Flask 3.1.3, gunicorn 26.2.0, Python 3.14.7) in 0.12 s (about 6 ms per request in a tight loop, 14 ms for a cold request), each leaving a RecursionError: Stack overflow ... while decoding a JSON array traceback in the error log.

Impact

An unauthenticated attacker can turn every request to a JWT validating endpoint into a server error with a full traceback logged per request, a cheap and repeatable denial of service on the authentication path (no crash, no data exposure).

Fix

Catch RecursionError alongside ValueError in _load() and raise DecodeError, or parse the header with a nonrecursive, depthbounded parser.

Reproduction

A standalone package (docker-compose.yml, Dockerfile, requirements.txt, target app, driver) accompanies this report:

cd <package dir>
docker compose up -d --build
python3 poc_check_then_attack.py
docker compose down -v

poc_pyjwt_recursion.zip

Exit 0= reproduced (control checks green, exactly one crafted request returns 500, traceback verified in docker logs, service alive afterwards); 1 = not reproduced; 2 = checks failed, no attack sent. The package's run_log.txt documents a complete proof run.

Credits

@Nivid42

Maintainer update — 2026-09-09

We reproduced the reported behavior on PyJWT 2.13.0: a deeply nested JSON array in the untrusted compact-JWS header reaches json.loads() before signature verification and raises RecursionError, which is not a PyJWTError. The same input is accepted by the public jwt.decode() path and can escape an application's normal except PyJWTError handling.

The fix is committed as 06573692ebcdec8831c3927513b3e87c31fbbb62. PyJWS._load() now translates both ValueError and RecursionError from header JSON parsing into DecodeError. A regression test covers the deeply nested-header path before signature verification. The full suite passes with 373 tests and 4 intentional cryptography-environment skips.

No release containing the fix has been published yet, so the patched version remains unset pending release planning. The advisory remains medium severity and unpublished.

Maintainer update — 2026-09-11

The verified fix for this advisory is included in PyJWT 2.14.0, released on 2026-09-11 and available on PyPI. PyJWT 2.14.0 is the first release containing the fix. This advisory is now published with 2.14.0 recorded as the patched version.

Severity

5.3 (Medium)


                    
                      CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

References

URL

Type

	https://github.com/jpadilla/pyjwt/security/adviso…	WEB
	https://nvd.nist.gov/vuln/detail/CVE-2026-102265	ADVISORY
	https://github.com/jpadilla/pyjwt/commit/06573692…	WEB
	https://github.com/jpadilla/pyjwt	PACKAGE
	https://github.com/jpadilla/pyjwt/releases/tag/2.14.0	WEB

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": "bump",
        "range_state": "fixed",
        "resource": "pyjwt",
        "resource_purl": "pkg:pypi/pyjwt@2.15.0",
        "upstream_fixed_in": "2.14.0"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "snowflake-cli",
        "purl": "pkg:brew/snowflake-cli"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.19.0"
            },
            {
              "fixed": "3.28.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/pyjwt@2.15.0",
        "name": "pyjwt",
        "resource": "pyjwt",
        "strategy": "registry",
        "subject_version": "2.15.0"
      }
    ]
  },
  "details": "## Package\n\npyjwt (PyPI)\n\n## Affected versions\n\ntested \u0026 verified on: 2.13.0. Every version whose `PyJWS._load()` translates only `ValueError` is affected\n\n## Description\n\n`PyJWS._looad()` (`jwt/api_jws.py:337`) splits the compact token, base64url decodes the header segment and hands it to `json.loads()` before `_verify_signature()` runs. The parse is wrapped in `except ValueError as e: raise DecodeError(...)`. That is what makes the documented contract sufficient for untrusted input: `except jwt.PyJWTError` (or `InvalidTokenError`) around `jwt.decode(token, key, algorithms=[...])`.\n\nCPython\u0027s JSON decoder raises `RecursionError` (a `RuntimeError` subclass, not a `ValueError`) once nesting crosses the native stack guard. That exception leaves `_load()`, then `jwt.decode()`, and matches no `PyJWTError` handlerr at all. No key and no valid signature are needed: the header is parsed first, so a single unauthenticated request with an unsigned token suffices.\n\nScope: the recursion threshold is ~65,000 nesting levels; below it the same input yields a clean `DecodeError` (a 346,800-byte flat header is rejected normally, so depth, not size, is the trigger). A token this large cannot ride in an `Authorization` header (rejected at HTTP field limits,431 under gunicorn), but body transport (RFC 7662 introspection style) is a standard pattern. Under Flask 3.1.3 / gunicorn 26.2.0 each crafted request returns HTTP 500 instead of 401 and writes a full traceback to the error log; the sync worker survives.\n\n## Proof of concept\n\nAgainst any endpoint that validates a token from its JSON body with the documented pattern:\n\n```python\nimport base64, json, http.client\n\ndef b64url(b): return base64.urlsafe_b64encode(b).rstrip(b\"=\")\n\n# unsigned token: the header segment is 200,000 nested \u0027[\u0027 (266,681 bytes total)\ntoken = (b64url(b\"[\" * 200_000) + b\".\" + b64url(b\u0027{\"a\":1}\u0027) + b\".\" + b64url(b\"x\")).decode()\n\nconn = http.client.HTTPConnection(\"127.0.0.1\", 8125, timeout=30)\nconn.request(\"POST\", \"/api/protected\", body=json.dumps({\"token\": token}),\n             headers={\"Content-Type\": \"application/json\"})\nprint(conn.getresponse().status)   # 500, expected 401\n```\n\nDeterminism: 20/20 crafted requests returned 500 against the reference container (PyJWT 2.13.0, Flask 3.1.3, gunicorn 26.2.0, Python 3.14.7) in 0.12 s (about 6 ms per request in a tight loop, 14 ms for a cold request), each leaving a `RecursionError: Stack overflow ... while decoding a JSON array` traceback in the error log.\n\n## Impact\n\nAn unauthenticated attacker can turn every request to a JWT validating endpoint into a server error with a full traceback logged per request, a cheap and repeatable denial of service on the authentication path (no crash, no data exposure).\n\n## Fix\n\nCatch `RecursionError` alongside `ValueError` in `_load()` and raise `DecodeError`, or parse the header with a nonrecursive, depthbounded parser.\n\n## Reproduction\n\nA standalone package (docker-compose.yml, Dockerfile, requirements.txt, target app, driver) accompanies this report:\n\n```\ncd \u003cpackage dir\u003e\ndocker compose up -d --build\npython3 poc_check_then_attack.py\ndocker compose down -v\n```\n[poc_pyjwt_recursion.zip](https://github.com/user-attachments/files/31614987/poc_pyjwt_recursion.zip)\n\nExit 0= reproduced (control checks green, exactly one crafted request returns 500, traceback verified in `docker logs`, service alive afterwards); 1 = not reproduced; 2 = checks failed, no attack sent. The package\u0027s `run_log.txt` documents a complete proof run.\n\n## Credits\n\n- @Nivid42\n\n## Maintainer update \u2014 2026-09-09\n\nWe reproduced the reported behavior on PyJWT 2.13.0: a deeply nested JSON array in the untrusted compact-JWS header reaches `json.loads()` before signature verification and raises `RecursionError`, which is not a `PyJWTError`. The same input is accepted by the public `jwt.decode()` path and can escape an application\u0027s normal `except PyJWTError` handling.\n\nThe fix is committed as `06573692ebcdec8831c3927513b3e87c31fbbb62`. `PyJWS._load()` now translates both `ValueError` and `RecursionError` from header JSON parsing into `DecodeError`. A regression test covers the deeply nested-header path before signature verification. The full suite passes with 373 tests and 4 intentional cryptography-environment skips.\n\nNo release containing the fix has been published yet, so the patched version remains unset pending release planning. The advisory remains medium severity and unpublished.\n\n## Maintainer update \u2014 2026-09-11\n\nThe verified fix for this advisory is included in PyJWT 2.14.0, released on 2026-09-11 and available on PyPI. PyJWT 2.14.0 is the first release containing the fix. This advisory is now published with 2.14.0 recorded as the patched version.",
  "id": "BREW-snowflake-cli-CVE-2026-102265",
  "modified": "2026-09-30T09:56:05Z",
  "published": "2026-09-30T09:56:05Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/security/advisories/GHSA-8wjv-2p76-3863"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-102265"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/commit/06573692ebcdec8831c3927513b3e87c31fbbb62"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/jpadilla/pyjwt"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/releases/tag/2.14.0"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "PyJWT: Uncaught RecursionError in jwt.decode() on deeply nested token header",
  "upstream": [
    "GHSA-8wjv-2p76-3863",
    "CVE-2026-102265"
  ]
}

BREW-SNYK-AGENT-SCAN-CVE… (GHSA-8WJV-2P76-3863)

Vulnerability from osv_homebrew – Published: 2026-09-30 09:42 – Updated: 2026-09-30 09:42 – Source website

Summary

PyJWT: Uncaught RecursionError in jwt.decode() on deeply nested token header

Details

Package

pyjwt (PyPI)

Affected versions

tested & verified on: 2.13.0. Every version whose PyJWS._load() translates only ValueError is affected

Description

PyJWS._looad() (jwt/api_jws.py:337) splits the compact token, base64url decodes the header segment and hands it to json.loads() before _verify_signature() runs. The parse is wrapped in except ValueError as e: raise DecodeError(...). That is what makes the documented contract sufficient for untrusted input: except jwt.PyJWTError (or InvalidTokenError) around jwt.decode(token, key, algorithms=[...]).

CPython's JSON decoder raises RecursionError (a RuntimeError subclass, not a ValueError) once nesting crosses the native stack guard. That exception leaves _load(), then jwt.decode(), and matches no PyJWTError handlerr at all. No key and no valid signature are needed: the header is parsed first, so a single unauthenticated request with an unsigned token suffices.

Scope: the recursion threshold is ~65,000 nesting levels; below it the same input yields a clean DecodeError (a 346,800-byte flat header is rejected normally, so depth, not size, is the trigger). A token this large cannot ride in an Authorization header (rejected at HTTP field limits,431 under gunicorn), but body transport (RFC 7662 introspection style) is a standard pattern. Under Flask 3.1.3 / gunicorn 26.2.0 each crafted request returns HTTP 500 instead of 401 and writes a full traceback to the error log; the sync worker survives.

Proof of concept

Against any endpoint that validates a token from its JSON body with the documented pattern:

import base64, json, http.client

def b64url(b): return base64.urlsafe_b64encode(b).rstrip(b"=")

# unsigned token: the header segment is 200,000 nested '[' (266,681 bytes total)
token = (b64url(b"[" * 200_000) + b"." + b64url(b'{"a":1}') + b"." + b64url(b"x")).decode()

conn = http.client.HTTPConnection("127.0.0.1", 8125, timeout=30)
conn.request("POST", "/api/protected", body=json.dumps({"token": token}),
             headers={"Content-Type": "application/json"})
print(conn.getresponse().status)   # 500, expected 401

Determinism: 20/20 crafted requests returned 500 against the reference container (PyJWT 2.13.0, Flask 3.1.3, gunicorn 26.2.0, Python 3.14.7) in 0.12 s (about 6 ms per request in a tight loop, 14 ms for a cold request), each leaving a RecursionError: Stack overflow ... while decoding a JSON array traceback in the error log.

Impact

An unauthenticated attacker can turn every request to a JWT validating endpoint into a server error with a full traceback logged per request, a cheap and repeatable denial of service on the authentication path (no crash, no data exposure).

Fix

Catch RecursionError alongside ValueError in _load() and raise DecodeError, or parse the header with a nonrecursive, depthbounded parser.

Reproduction

A standalone package (docker-compose.yml, Dockerfile, requirements.txt, target app, driver) accompanies this report:

cd <package dir>
docker compose up -d --build
python3 poc_check_then_attack.py
docker compose down -v

poc_pyjwt_recursion.zip

Exit 0= reproduced (control checks green, exactly one crafted request returns 500, traceback verified in docker logs, service alive afterwards); 1 = not reproduced; 2 = checks failed, no attack sent. The package's run_log.txt documents a complete proof run.

Credits

@Nivid42

Maintainer update — 2026-09-09

We reproduced the reported behavior on PyJWT 2.13.0: a deeply nested JSON array in the untrusted compact-JWS header reaches json.loads() before signature verification and raises RecursionError, which is not a PyJWTError. The same input is accepted by the public jwt.decode() path and can escape an application's normal except PyJWTError handling.

The fix is committed as 06573692ebcdec8831c3927513b3e87c31fbbb62. PyJWS._load() now translates both ValueError and RecursionError from header JSON parsing into DecodeError. A regression test covers the deeply nested-header path before signature verification. The full suite passes with 373 tests and 4 intentional cryptography-environment skips.

No release containing the fix has been published yet, so the patched version remains unset pending release planning. The advisory remains medium severity and unpublished.

Maintainer update — 2026-09-11

The verified fix for this advisory is included in PyJWT 2.14.0, released on 2026-09-11 and available on PyPI. PyJWT 2.14.0 is the first release containing the fix. This advisory is now published with 2.14.0 recorded as the patched version.

Severity

5.3 (Medium)


                    
                      CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

References

URL

Type

	https://github.com/jpadilla/pyjwt/security/adviso…	WEB
	https://nvd.nist.gov/vuln/detail/CVE-2026-102265	ADVISORY
	https://github.com/jpadilla/pyjwt/commit/06573692…	WEB
	https://github.com/jpadilla/pyjwt	PACKAGE
	https://github.com/jpadilla/pyjwt/releases/tag/2.14.0	WEB

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": "bump",
        "range_state": "fixed",
        "resource": "pyjwt",
        "resource_purl": "pkg:pypi/pyjwt@2.15.0",
        "upstream_fixed_in": "2.14.0"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "snyk-agent-scan",
        "purl": "pkg:brew/snyk-agent-scan"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.5.4_1"
            },
            {
              "fixed": "0.6.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/pyjwt@2.15.0",
        "name": "pyjwt",
        "resource": "pyjwt",
        "strategy": "registry",
        "subject_version": "2.15.0"
      }
    ]
  },
  "details": "## Package\n\npyjwt (PyPI)\n\n## Affected versions\n\ntested \u0026 verified on: 2.13.0. Every version whose `PyJWS._load()` translates only `ValueError` is affected\n\n## Description\n\n`PyJWS._looad()` (`jwt/api_jws.py:337`) splits the compact token, base64url decodes the header segment and hands it to `json.loads()` before `_verify_signature()` runs. The parse is wrapped in `except ValueError as e: raise DecodeError(...)`. That is what makes the documented contract sufficient for untrusted input: `except jwt.PyJWTError` (or `InvalidTokenError`) around `jwt.decode(token, key, algorithms=[...])`.\n\nCPython\u0027s JSON decoder raises `RecursionError` (a `RuntimeError` subclass, not a `ValueError`) once nesting crosses the native stack guard. That exception leaves `_load()`, then `jwt.decode()`, and matches no `PyJWTError` handlerr at all. No key and no valid signature are needed: the header is parsed first, so a single unauthenticated request with an unsigned token suffices.\n\nScope: the recursion threshold is ~65,000 nesting levels; below it the same input yields a clean `DecodeError` (a 346,800-byte flat header is rejected normally, so depth, not size, is the trigger). A token this large cannot ride in an `Authorization` header (rejected at HTTP field limits,431 under gunicorn), but body transport (RFC 7662 introspection style) is a standard pattern. Under Flask 3.1.3 / gunicorn 26.2.0 each crafted request returns HTTP 500 instead of 401 and writes a full traceback to the error log; the sync worker survives.\n\n## Proof of concept\n\nAgainst any endpoint that validates a token from its JSON body with the documented pattern:\n\n```python\nimport base64, json, http.client\n\ndef b64url(b): return base64.urlsafe_b64encode(b).rstrip(b\"=\")\n\n# unsigned token: the header segment is 200,000 nested \u0027[\u0027 (266,681 bytes total)\ntoken = (b64url(b\"[\" * 200_000) + b\".\" + b64url(b\u0027{\"a\":1}\u0027) + b\".\" + b64url(b\"x\")).decode()\n\nconn = http.client.HTTPConnection(\"127.0.0.1\", 8125, timeout=30)\nconn.request(\"POST\", \"/api/protected\", body=json.dumps({\"token\": token}),\n             headers={\"Content-Type\": \"application/json\"})\nprint(conn.getresponse().status)   # 500, expected 401\n```\n\nDeterminism: 20/20 crafted requests returned 500 against the reference container (PyJWT 2.13.0, Flask 3.1.3, gunicorn 26.2.0, Python 3.14.7) in 0.12 s (about 6 ms per request in a tight loop, 14 ms for a cold request), each leaving a `RecursionError: Stack overflow ... while decoding a JSON array` traceback in the error log.\n\n## Impact\n\nAn unauthenticated attacker can turn every request to a JWT validating endpoint into a server error with a full traceback logged per request, a cheap and repeatable denial of service on the authentication path (no crash, no data exposure).\n\n## Fix\n\nCatch `RecursionError` alongside `ValueError` in `_load()` and raise `DecodeError`, or parse the header with a nonrecursive, depthbounded parser.\n\n## Reproduction\n\nA standalone package (docker-compose.yml, Dockerfile, requirements.txt, target app, driver) accompanies this report:\n\n```\ncd \u003cpackage dir\u003e\ndocker compose up -d --build\npython3 poc_check_then_attack.py\ndocker compose down -v\n```\n[poc_pyjwt_recursion.zip](https://github.com/user-attachments/files/31614987/poc_pyjwt_recursion.zip)\n\nExit 0= reproduced (control checks green, exactly one crafted request returns 500, traceback verified in `docker logs`, service alive afterwards); 1 = not reproduced; 2 = checks failed, no attack sent. The package\u0027s `run_log.txt` documents a complete proof run.\n\n## Credits\n\n- @Nivid42\n\n## Maintainer update \u2014 2026-09-09\n\nWe reproduced the reported behavior on PyJWT 2.13.0: a deeply nested JSON array in the untrusted compact-JWS header reaches `json.loads()` before signature verification and raises `RecursionError`, which is not a `PyJWTError`. The same input is accepted by the public `jwt.decode()` path and can escape an application\u0027s normal `except PyJWTError` handling.\n\nThe fix is committed as `06573692ebcdec8831c3927513b3e87c31fbbb62`. `PyJWS._load()` now translates both `ValueError` and `RecursionError` from header JSON parsing into `DecodeError`. A regression test covers the deeply nested-header path before signature verification. The full suite passes with 373 tests and 4 intentional cryptography-environment skips.\n\nNo release containing the fix has been published yet, so the patched version remains unset pending release planning. The advisory remains medium severity and unpublished.\n\n## Maintainer update \u2014 2026-09-11\n\nThe verified fix for this advisory is included in PyJWT 2.14.0, released on 2026-09-11 and available on PyPI. PyJWT 2.14.0 is the first release containing the fix. This advisory is now published with 2.14.0 recorded as the patched version.",
  "id": "BREW-snyk-agent-scan-CVE-2026-102265",
  "modified": "2026-09-30T09:42:19Z",
  "published": "2026-09-30T09:42:19Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/security/advisories/GHSA-8wjv-2p76-3863"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-102265"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/commit/06573692ebcdec8831c3927513b3e87c31fbbb62"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/jpadilla/pyjwt"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/releases/tag/2.14.0"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "PyJWT: Uncaught RecursionError in jwt.decode() on deeply nested token header",
  "upstream": [
    "GHSA-8wjv-2p76-3863",
    "CVE-2026-102265"
  ]
}

BREW-STRANDS-AGENTS-SOPS… (GHSA-8WJV-2P76-3863)

Vulnerability from osv_homebrew – Published: 2026-09-30 09:58 – Updated: 2026-09-30 09:58 – Source website

Summary

PyJWT: Uncaught RecursionError in jwt.decode() on deeply nested token header

Details

Package

pyjwt (PyPI)

Affected versions

tested & verified on: 2.13.0. Every version whose PyJWS._load() translates only ValueError is affected

Description

PyJWS._looad() (jwt/api_jws.py:337) splits the compact token, base64url decodes the header segment and hands it to json.loads() before _verify_signature() runs. The parse is wrapped in except ValueError as e: raise DecodeError(...). That is what makes the documented contract sufficient for untrusted input: except jwt.PyJWTError (or InvalidTokenError) around jwt.decode(token, key, algorithms=[...]).

CPython's JSON decoder raises RecursionError (a RuntimeError subclass, not a ValueError) once nesting crosses the native stack guard. That exception leaves _load(), then jwt.decode(), and matches no PyJWTError handlerr at all. No key and no valid signature are needed: the header is parsed first, so a single unauthenticated request with an unsigned token suffices.

Scope: the recursion threshold is ~65,000 nesting levels; below it the same input yields a clean DecodeError (a 346,800-byte flat header is rejected normally, so depth, not size, is the trigger). A token this large cannot ride in an Authorization header (rejected at HTTP field limits,431 under gunicorn), but body transport (RFC 7662 introspection style) is a standard pattern. Under Flask 3.1.3 / gunicorn 26.2.0 each crafted request returns HTTP 500 instead of 401 and writes a full traceback to the error log; the sync worker survives.

Proof of concept

Against any endpoint that validates a token from its JSON body with the documented pattern:

import base64, json, http.client

def b64url(b): return base64.urlsafe_b64encode(b).rstrip(b"=")

# unsigned token: the header segment is 200,000 nested '[' (266,681 bytes total)
token = (b64url(b"[" * 200_000) + b"." + b64url(b'{"a":1}') + b"." + b64url(b"x")).decode()

conn = http.client.HTTPConnection("127.0.0.1", 8125, timeout=30)
conn.request("POST", "/api/protected", body=json.dumps({"token": token}),
             headers={"Content-Type": "application/json"})
print(conn.getresponse().status)   # 500, expected 401

Determinism: 20/20 crafted requests returned 500 against the reference container (PyJWT 2.13.0, Flask 3.1.3, gunicorn 26.2.0, Python 3.14.7) in 0.12 s (about 6 ms per request in a tight loop, 14 ms for a cold request), each leaving a RecursionError: Stack overflow ... while decoding a JSON array traceback in the error log.

Impact

An unauthenticated attacker can turn every request to a JWT validating endpoint into a server error with a full traceback logged per request, a cheap and repeatable denial of service on the authentication path (no crash, no data exposure).

Fix

Catch RecursionError alongside ValueError in _load() and raise DecodeError, or parse the header with a nonrecursive, depthbounded parser.

Reproduction

A standalone package (docker-compose.yml, Dockerfile, requirements.txt, target app, driver) accompanies this report:

cd <package dir>
docker compose up -d --build
python3 poc_check_then_attack.py
docker compose down -v

poc_pyjwt_recursion.zip

Exit 0= reproduced (control checks green, exactly one crafted request returns 500, traceback verified in docker logs, service alive afterwards); 1 = not reproduced; 2 = checks failed, no attack sent. The package's run_log.txt documents a complete proof run.

Credits

@Nivid42

Maintainer update — 2026-09-09

We reproduced the reported behavior on PyJWT 2.13.0: a deeply nested JSON array in the untrusted compact-JWS header reaches json.loads() before signature verification and raises RecursionError, which is not a PyJWTError. The same input is accepted by the public jwt.decode() path and can escape an application's normal except PyJWTError handling.

The fix is committed as 06573692ebcdec8831c3927513b3e87c31fbbb62. PyJWS._load() now translates both ValueError and RecursionError from header JSON parsing into DecodeError. A regression test covers the deeply nested-header path before signature verification. The full suite passes with 373 tests and 4 intentional cryptography-environment skips.

No release containing the fix has been published yet, so the patched version remains unset pending release planning. The advisory remains medium severity and unpublished.

Maintainer update — 2026-09-11

The verified fix for this advisory is included in PyJWT 2.14.0, released on 2026-09-11 and available on PyPI. PyJWT 2.14.0 is the first release containing the fix. This advisory is now published with 2.14.0 recorded as the patched version.

Severity

5.3 (Medium)


                    
                      CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

References

URL

Type

	https://github.com/jpadilla/pyjwt/security/adviso…	WEB
	https://nvd.nist.gov/vuln/detail/CVE-2026-102265	ADVISORY
	https://github.com/jpadilla/pyjwt/commit/06573692…	WEB
	https://github.com/jpadilla/pyjwt	PACKAGE
	https://github.com/jpadilla/pyjwt/releases/tag/2.14.0	WEB

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": null,
        "range_state": "affected",
        "resource": "pyjwt",
        "resource_purl": "pkg:pypi/pyjwt@2.13.0",
        "upstream_fixed_in": "2.14.0"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "strands-agents-sops",
        "purl": "pkg:brew/strands-agents-sops"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.1.2_3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/pyjwt@2.13.0",
        "name": "pyjwt",
        "resource": "pyjwt",
        "strategy": "registry",
        "subject_version": "2.13.0"
      }
    ]
  },
  "details": "## Package\n\npyjwt (PyPI)\n\n## Affected versions\n\ntested \u0026 verified on: 2.13.0. Every version whose `PyJWS._load()` translates only `ValueError` is affected\n\n## Description\n\n`PyJWS._looad()` (`jwt/api_jws.py:337`) splits the compact token, base64url decodes the header segment and hands it to `json.loads()` before `_verify_signature()` runs. The parse is wrapped in `except ValueError as e: raise DecodeError(...)`. That is what makes the documented contract sufficient for untrusted input: `except jwt.PyJWTError` (or `InvalidTokenError`) around `jwt.decode(token, key, algorithms=[...])`.\n\nCPython\u0027s JSON decoder raises `RecursionError` (a `RuntimeError` subclass, not a `ValueError`) once nesting crosses the native stack guard. That exception leaves `_load()`, then `jwt.decode()`, and matches no `PyJWTError` handlerr at all. No key and no valid signature are needed: the header is parsed first, so a single unauthenticated request with an unsigned token suffices.\n\nScope: the recursion threshold is ~65,000 nesting levels; below it the same input yields a clean `DecodeError` (a 346,800-byte flat header is rejected normally, so depth, not size, is the trigger). A token this large cannot ride in an `Authorization` header (rejected at HTTP field limits,431 under gunicorn), but body transport (RFC 7662 introspection style) is a standard pattern. Under Flask 3.1.3 / gunicorn 26.2.0 each crafted request returns HTTP 500 instead of 401 and writes a full traceback to the error log; the sync worker survives.\n\n## Proof of concept\n\nAgainst any endpoint that validates a token from its JSON body with the documented pattern:\n\n```python\nimport base64, json, http.client\n\ndef b64url(b): return base64.urlsafe_b64encode(b).rstrip(b\"=\")\n\n# unsigned token: the header segment is 200,000 nested \u0027[\u0027 (266,681 bytes total)\ntoken = (b64url(b\"[\" * 200_000) + b\".\" + b64url(b\u0027{\"a\":1}\u0027) + b\".\" + b64url(b\"x\")).decode()\n\nconn = http.client.HTTPConnection(\"127.0.0.1\", 8125, timeout=30)\nconn.request(\"POST\", \"/api/protected\", body=json.dumps({\"token\": token}),\n             headers={\"Content-Type\": \"application/json\"})\nprint(conn.getresponse().status)   # 500, expected 401\n```\n\nDeterminism: 20/20 crafted requests returned 500 against the reference container (PyJWT 2.13.0, Flask 3.1.3, gunicorn 26.2.0, Python 3.14.7) in 0.12 s (about 6 ms per request in a tight loop, 14 ms for a cold request), each leaving a `RecursionError: Stack overflow ... while decoding a JSON array` traceback in the error log.\n\n## Impact\n\nAn unauthenticated attacker can turn every request to a JWT validating endpoint into a server error with a full traceback logged per request, a cheap and repeatable denial of service on the authentication path (no crash, no data exposure).\n\n## Fix\n\nCatch `RecursionError` alongside `ValueError` in `_load()` and raise `DecodeError`, or parse the header with a nonrecursive, depthbounded parser.\n\n## Reproduction\n\nA standalone package (docker-compose.yml, Dockerfile, requirements.txt, target app, driver) accompanies this report:\n\n```\ncd \u003cpackage dir\u003e\ndocker compose up -d --build\npython3 poc_check_then_attack.py\ndocker compose down -v\n```\n[poc_pyjwt_recursion.zip](https://github.com/user-attachments/files/31614987/poc_pyjwt_recursion.zip)\n\nExit 0= reproduced (control checks green, exactly one crafted request returns 500, traceback verified in `docker logs`, service alive afterwards); 1 = not reproduced; 2 = checks failed, no attack sent. The package\u0027s `run_log.txt` documents a complete proof run.\n\n## Credits\n\n- @Nivid42\n\n## Maintainer update \u2014 2026-09-09\n\nWe reproduced the reported behavior on PyJWT 2.13.0: a deeply nested JSON array in the untrusted compact-JWS header reaches `json.loads()` before signature verification and raises `RecursionError`, which is not a `PyJWTError`. The same input is accepted by the public `jwt.decode()` path and can escape an application\u0027s normal `except PyJWTError` handling.\n\nThe fix is committed as `06573692ebcdec8831c3927513b3e87c31fbbb62`. `PyJWS._load()` now translates both `ValueError` and `RecursionError` from header JSON parsing into `DecodeError`. A regression test covers the deeply nested-header path before signature verification. The full suite passes with 373 tests and 4 intentional cryptography-environment skips.\n\nNo release containing the fix has been published yet, so the patched version remains unset pending release planning. The advisory remains medium severity and unpublished.\n\n## Maintainer update \u2014 2026-09-11\n\nThe verified fix for this advisory is included in PyJWT 2.14.0, released on 2026-09-11 and available on PyPI. PyJWT 2.14.0 is the first release containing the fix. This advisory is now published with 2.14.0 recorded as the patched version.",
  "id": "BREW-strands-agents-sops-CVE-2026-102265",
  "modified": "2026-09-30T09:58:03Z",
  "published": "2026-09-30T09:58:03Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/security/advisories/GHSA-8wjv-2p76-3863"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-102265"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/commit/06573692ebcdec8831c3927513b3e87c31fbbb62"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/jpadilla/pyjwt"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/releases/tag/2.14.0"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "PyJWT: Uncaught RecursionError in jwt.decode() on deeply nested token header",
  "upstream": [
    "GHSA-8wjv-2p76-3863",
    "CVE-2026-102265"
  ]
}

FKIE_CVE-2026-102265

Vulnerability from fkie_nvd - Published: 2026-09-28 21:17 - Updated: 2026-09-30 19:38

Severity

5.3 (Medium) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Summary

PyJWT is a Python implementation of JSON Web Token standards. From 2.13.0 until 2.14.0, PyJWS._load in jwt/api_jws.py is affected because parser catches ValueError but not RecursionError. This occurs when a deeply nested token header reaches json.loads. As a result, RecursionError escapes the documented PyJWT error hierarchy. Consequently, an unauthenticated malformed token can cause a request-level failure and HTTP 500. This issue is fixed in version 2.14.0.

References

	URL	Tags
	security-advisories@github.com	https://github.com/jpadilla/pyjwt/commit/06573692ebcdec8831c3927513b3e87c31fbbb62
	security-advisories@github.com	https://github.com/jpadilla/pyjwt/releases/tag/2.14.0
	security-advisories@github.com	https://github.com/jpadilla/pyjwt/security/advisories/GHSA-8wjv-2p76-3863

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "pyjwt",
          "vendor": "jpadilla",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 2.13.0, \u003c 2.14.0"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "PyJWT is a Python implementation of JSON Web Token standards. From 2.13.0 until 2.14.0, PyJWS._load in jwt/api_jws.py is affected because parser catches ValueError but not RecursionError. This occurs when a deeply nested token header reaches json.loads. As a result, RecursionError escapes the documented PyJWT error hierarchy. Consequently, an unauthenticated malformed token can cause a request-level failure and HTTP 500. This issue is fixed in version 2.14.0."
    }
  ],
  "id": "CVE-2026-102265",
  "lastModified": "2026-09-30T19:38:27.293",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "LOW",
          "baseScore": 5.3,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
          "version": "3.1"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 1.4,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-09-28T21:17:14.077",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/jpadilla/pyjwt/commit/06573692ebcdec8831c3927513b3e87c31fbbb62"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/jpadilla/pyjwt/releases/tag/2.14.0"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/jpadilla/pyjwt/security/advisories/GHSA-8wjv-2p76-3863"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Awaiting Analysis",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-674"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Primary"
    }
  ]
}

CVE-2026-102265 (GCVE-0-2026-102265)

Tags

Sightings

Nomenclature

Related by attack behaviour

Action not permitted

CVE-2026-102265 (GCVE-0-2026-102265)

BREW-MCP-PROXY-CVE-2026-102265 (GHSA-8WJV-2P76-3863)

Package

Affected versions

Description

Proof of concept

Impact

Fix

Reproduction

Credits

Maintainer update — 2026-09-09

Maintainer update — 2026-09-11

BREW-MISTRAL-VIBE-CVE-20… (GHSA-8WJV-2P76-3863)

Package

Affected versions

Description

Proof of concept

Impact

Fix

Reproduction

Credits

Maintainer update — 2026-09-09

Maintainer update — 2026-09-11

BREW-OCI-CLI-CVE-2026-102265 (GHSA-8WJV-2P76-3863)

Package

Affected versions

Description

Proof of concept

Impact

Fix

Reproduction

Credits

Maintainer update — 2026-09-09

Maintainer update — 2026-09-11

BREW-OTERM-CVE-2026-102265 (GHSA-8WJV-2P76-3863)

Package

Affected versions

Description

Proof of concept

Impact

Fix

Reproduction

Credits

Maintainer update — 2026-09-09

Maintainer update — 2026-09-11

BREW-RAPID-MLX-CVE-2026-102265 (GHSA-8WJV-2P76-3863)

Package

Affected versions

Description

Proof of concept

Impact

Fix

Reproduction

Credits

Maintainer update — 2026-09-09

Maintainer update — 2026-09-11

BREW-SIGSTORE-CVE-2026-102265 (GHSA-8WJV-2P76-3863)

Package

Affected versions

Description

Proof of concept

Impact

Fix

Reproduction

Credits

Maintainer update — 2026-09-09

Maintainer update — 2026-09-11

BREW-SNOWFLAKE-CLI-CVE-2… (GHSA-8WJV-2P76-3863)

Package

Affected versions

Description

Proof of concept

Impact

Fix

Reproduction

Credits

Maintainer update — 2026-09-09

Maintainer update — 2026-09-11

BREW-SNYK-AGENT-SCAN-CVE… (GHSA-8WJV-2P76-3863)