Vulnerability-Lookup

CVE-2026-100351 (GCVE-0-2026-100351)

Vulnerability from cvelistv5 – Published: 2026-10-15 15:52 – Updated: 2026-10-15 16:09

Title

kin-openapi: ValidationHandler security-requirement bypass via encoded-path operation confusion

Summary

kin-openapi is a Go project for handling OpenAPI files. From 0.144.0 until 0.147.0, openapi3filter.ValidationHandler validates an operation selected from decoded URL.Path while a downstream gorilla/mux router configured with UseEncodedPath can dispatch a different operation selected from URL.RawPath. When a public exact route and a protected parameterized route use the same method and overlap after decoding, an unauthenticated remote request containing an encoded path separator can be validated as public and then dispatched to the protected handler without invoking the configured AuthenticationFunc. The reachable path parameter is constrained to an encoded representation that decodes to the public literal route, and proxies that canonicalize the URI before forwarding prevent this specific mismatch. This issue is fixed in version 0.147.0.

Severity

7.4 (High)


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

SSVC

Exploitation: poc Automatable: no Technical Impact: total

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-10-15 16:09 UTC

CWE

CWE-289 - Authentication Bypass by Alternate Name
CWE-436 - Interpretation Conflict

Assigner

GitHub_M CNA under the mitre root

CNA scorecard C 72/100 over 7712 records in the last 180 days details

References

3 references

URL	Tags
https://github.com/getkin/kin-openapi/security/ad…	x_refsource_CONFIRM
https://github.com/getkin/kin-openapi/commit/eda8…	x_refsource_MISC
https://github.com/getkin/kin-openapi/releases/ta…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
getkin	kin-openapi	Affected: >= 0.144.0, < 0.147.0	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-100351

Vulnerability from fkie_nvd - Published: 2026-10-15 16:17 - Updated: 2026-10-15 17:17

Severity

7.4 (High) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/getkin/kin-openapi/commit/eda80e2676e9f577ceed2dd80e64f16083edb041
	security-advisories@github.com	https://github.com/getkin/kin-openapi/releases/tag/v0.147.0
	security-advisories@github.com	https://github.com/getkin/kin-openapi/security/advisories/GHSA-23vg-4cjm-66q5
	134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/getkin/kin-openapi/security/advisories/GHSA-23vg-4cjm-66q5

Impacted products

	Vendor	Product	Version

JSON

To clipboard

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}

GHSA-23VG-4CJM-66Q5

Vulnerability from github – Published: 2026-10-15 20:19 – Updated: 2026-10-15 20:19

Summary

kin-openapi: ValidationHandler security-requirement bypass via encoded-path operation confusion

Details

Summary

openapi3filter.ValidationHandler.Middleware validates requests with kin-openapi's legacy router, which selects an OpenAPI operation from the decoded URL.Path. The method is documented as implementing gorilla/mux.MiddlewareFunc, but a downstream gorilla/mux router configured with UseEncodedPath() selects its handler from the encoded representation (URL.RawPath).

An unauthenticated request such as /public%2Fstatus can therefore be validated as an intentionally public operation (/public/status) and then dispatched to a protected operation (/{id}). The configured, rejecting AuthenticationFunc is never invoked, and the protected downstream handler runs.

This is distinct from GHSA-r277-6w6q-xmqw. The behavior below uses an explicit authentication callback that rejects missing credentials and remains reproducible after the v0.144.0 fix for the unsafe default callback.

Affected products

Product: github.com/getkin/kin-openapi
Component: openapi3filter.ValidationHandler.Middleware
Confirmed post-GHSA affected releases: v0.144.0, v0.145.0, and v0.146.0
Reporter attestation: each listed release was checked out separately, the attached single-file test was copied into openapi3filter/, and that test passed; maintainers should independently confirm the version range
Confirmed affected development revision: d33e44e67734dcde81b576582185e1343fb3985d
v0.143.0 also reproduces this mechanism, but GHSA-r277-6w6q-xmqw already provides a simpler bypass on that release; the distinct post-fix claim starts at v0.144.0
Earlier releases: not tested; please treat the introduction boundary as unknown

Security impact

An unauthenticated remote requester can reach a handler whose OpenAPI operation requires authentication when all of the following are true:

the application uses ValidationHandler.Middleware as the security gate;
the downstream router preserves and interprets an encoded path, such as gorilla/mux with UseEncodedPath();
a public exact route and a protected parameterized route overlap after decoding;
the public and protected operations expose the same HTTP method;
the protected handler relies on the validation layer's security decision.

The protected operation's path-parameter value is constrained: it is an encoded representation that decodes to a public literal path (public%2Fstatus in this PoC), not an arbitrary attacker-selected identifier. A protected operation without a compatible parameterized path is not reachable through this specific mechanism.

Primitive: the security decision is made for a different OpenAPI operation than the operation dispatched by the application router.
Demonstrated impact: a protected handler executes while the explicitly rejecting AuthenticationFunc is never invoked.
Impact ceiling: confidentiality or integrity loss when the reachable protected handler has that authority; the PoC does not demonstrate data disclosure or state modification.
Availability impact: not demonstrated.

Root cause

At the confirmed development revision:

openapi3filter/validation_handler.go: ValidationHandler.Load constructs routers/legacy.NewRouter unconditionally.
routers/legacy/router.go: route selection uses the decoded request path.
routers/gorillamux/router.go: the kin-openapi gorilla router constructs a gorilla/mux router with UseEncodedPath().
ValidationHandler.Middleware forwards the unchanged request after validation.

The component making the authentication decision and the component dispatching the handler can therefore disagree about the selected operation.

Reproduction

The attached PoC uses a real net/http server, an explicit API-key callback that rejects missing credentials, and a downstream gorilla/mux router with UseEncodedPath().

From a kin-openapi checkout, copy the self-contained attachment encoded_path_route_confusion_test.go.txt into openapi3filter/ as encoded_path_route_confusion_test.go, then run:

go test -v ./openapi3filter -run '^TestEncodedPathAuthorizationBypass$' -count=1

Expected attack observation:

status=202 downstream_route=/{id} protected_id=public%2Fstatus authentication_calls=0
wiring=Router.Use status=202 downstream_route=/{id} protected_id=public%2Fstatus authentication_calls=0

Controls included in the test show that:

/ordinary selects the protected operation, invokes authentication once, and is rejected with HTTP 401;
/public/status reaches only the intentionally public handler;
the encoded request reaches the protected /{id} handler with HTTP 202 while the authentication callback remains uncalled;
both external wrapping and the documented router.Use(validationHandler.Middleware) wiring reproduce the same result.

Reverse-proxy reachability

The same request was reproduced through Nginx 1.31.3 using the official nginx:alpine image digest sha256:4a73073bd557c65b759505da037898b61f1be6cbcc3c2c3aeac22d2a470c1752.

The exact container invocation was:

docker run --rm --name kin-openapi-nginx \
  --add-host=host.docker.internal:host-gateway \
  -p 18081:8080 -p 18082:8081 \
  -v "$PWD/poc/nginx.conf:/etc/nginx/nginx.conf:ro" \
  nginx:alpine

Container port 8080 uses proxy_pass http://host.docker.internal:18080; without a replacement URI. Host port 18081 therefore preserved /public%2Fstatus; the protected handler returned HTTP 202 and the authentication callback remained at zero calls. With proxy_pass http://host.docker.internal:18080/; on container port 8081 / host port 18082, Nginx canonicalized the upstream URI; both layers selected /public/status and the bypass did not occur.

Nginx access-log observations:

server_port=8080 "GET /public%2Fstatus HTTP/1.1" 202 0 "curl/8.7.1"
server_port=8081 "GET /public%2Fstatus HTTP/1.1" 204 0 "curl/8.7.1"
server_port=8080 "GET /ordinary HTTP/1.1" 401 0 "curl/8.7.1"

The response route headers were X-Poc-Route: /{id} on the preserving listener and X-Poc-Route: /public/status on the canonicalizing listener. Backend observations for the two requests were:

request_uri="/public%2Fstatus" path="/public/status" raw_path="/public%2Fstatus" auth_before=0
completed request_uri="/public%2Fstatus" auth_after=0
request_uri="/public/status" path="/public/status" raw_path="" auth_before=0
completed request_uri="/public/status" auth_after=0

This control shows that upstream path handling is a deployment precondition rather than claiming that every proxy configuration is affected.

The canonical protected control produced:

request_uri="/ordinary" path="/ordinary" raw_path="" auth_before=0
completed request_uri="/ordinary" auth_after=1

Suggested remediation

The authentication layer and downstream dispatcher must select the same OpenAPI operation from the same request representation.

Potential approaches:

make ValidationHandler accept a caller-supplied routers.Router and require it to match downstream routing semantics;
document that NewValidator already accepts a router but is safe only when the supplied router selects operations using the same semantics as the dispatcher; callers must also supply an AuthenticationFunc through ValidationOptions, or protected requests fail with the existing missing-authentication-service error;
as an interim hardening option, make ValidationHandler fail closed on an encoded path separator when URL.Path and URL.RawPath can select different operations, and verify this behavior against the full suite;
document the route-identity requirement and add encoded-separator regression tests.

Replacing the legacy router with the kin-openapi gorilla router closes this PoC, but a local compatibility check changed two existing missing-path-parameter tests from HTTP 400 semantics to route-not-found HTTP 404 semantics. A direct router swap is therefore not a fully validated drop-in fix.

Public-reference triage

The public advisory list and related path-encoding reports reviewed on 2026-08-18 did not describe this authentication-boundary crossing. Relevant nearby reports include issues #397, #1089, and #1105 and PR #400. This search is not proof of novelty; please deduplicate against private reports.

Credit

Preferred credit: Satoru Kanno (GMO CONNECT Inc., GMO Internet Group, Inc.)

Severity

7.4 (High)


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

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/getkin/kin-openapi"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.144.0"
            },
            {
              "fixed": "0.147.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-100351"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-289",
      "CWE-436"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-10-15T20:19:20Z",
    "nvd_published_at": "2026-10-15T16:17:31Z",
    "severity": "HIGH"
  },
  "details": "## Summary\n\n`openapi3filter.ValidationHandler.Middleware` validates requests with kin-openapi\u0027s\nlegacy router, which selects an OpenAPI operation from the decoded `URL.Path`. The\nmethod is documented as implementing `gorilla/mux.MiddlewareFunc`, but a downstream\ngorilla/mux router configured with `UseEncodedPath()` selects its handler from the\nencoded representation (`URL.RawPath`).\n\nAn unauthenticated request such as `/public%2Fstatus` can therefore be validated as an\nintentionally public operation (`/public/status`) and then dispatched to a protected\noperation (`/{id}`). The configured, rejecting `AuthenticationFunc` is never invoked,\nand the protected downstream handler runs.\n\nThis is distinct from GHSA-r277-6w6q-xmqw. The behavior below uses an explicit\nauthentication callback that rejects missing credentials and remains reproducible\nafter the v0.144.0 fix for the unsafe default callback.\n\n## Affected products\n\n- Product: `github.com/getkin/kin-openapi`\n- Component: `openapi3filter.ValidationHandler.Middleware`\n- Confirmed post-GHSA affected releases: v0.144.0, v0.145.0, and v0.146.0\n- Reporter attestation: each listed release was checked out separately, the attached\n  single-file test was copied into `openapi3filter/`, and that test passed; maintainers\n  should independently confirm the version range\n- Confirmed affected development revision: `d33e44e67734dcde81b576582185e1343fb3985d`\n- v0.143.0 also reproduces this mechanism, but GHSA-r277-6w6q-xmqw already provides a\n  simpler bypass on that release; the distinct post-fix claim starts at v0.144.0\n- Earlier releases: not tested; please treat the introduction boundary as unknown\n\n## Security impact\n\nAn unauthenticated remote requester can reach a handler whose OpenAPI operation\nrequires authentication when all of the following are true:\n\n1. the application uses `ValidationHandler.Middleware` as the security gate;\n2. the downstream router preserves and interprets an encoded path, such as\n   gorilla/mux with `UseEncodedPath()`;\n3. a public exact route and a protected parameterized route overlap after decoding;\n4. the public and protected operations expose the same HTTP method;\n5. the protected handler relies on the validation layer\u0027s security decision.\n\nThe protected operation\u0027s path-parameter value is constrained: it is an encoded\nrepresentation that decodes to a public literal path (`public%2Fstatus` in this PoC),\nnot an arbitrary attacker-selected identifier. A protected operation without a\ncompatible parameterized path is not reachable through this specific mechanism.\n\n- Primitive: the security decision is made for a different OpenAPI operation than the\n  operation dispatched by the application router.\n- Demonstrated impact: a protected handler executes while the explicitly rejecting\n  `AuthenticationFunc` is never invoked.\n- Impact ceiling: confidentiality or integrity loss when the reachable protected\n  handler has that authority; the PoC does not demonstrate data disclosure or state\n  modification.\n- Availability impact: not demonstrated.\n\n## Root cause\n\nAt the confirmed development revision:\n\n- `openapi3filter/validation_handler.go`: `ValidationHandler.Load` constructs\n  `routers/legacy.NewRouter` unconditionally.\n- `routers/legacy/router.go`: route selection uses the decoded request path.\n- `routers/gorillamux/router.go`: the kin-openapi gorilla router constructs a\n  gorilla/mux router with `UseEncodedPath()`.\n- `ValidationHandler.Middleware` forwards the unchanged request after validation.\n\nThe component making the authentication decision and the component dispatching the\nhandler can therefore disagree about the selected operation.\n\n## Reproduction\n\nThe attached PoC uses a real `net/http` server, an explicit API-key callback that\nrejects missing credentials, and a downstream gorilla/mux router with\n`UseEncodedPath()`.\n\nFrom a kin-openapi checkout, copy the self-contained attachment\n`encoded_path_route_confusion_test.go.txt` into `openapi3filter/` as\n`encoded_path_route_confusion_test.go`, then run:\n\n```sh\ngo test -v ./openapi3filter -run \u0027^TestEncodedPathAuthorizationBypass$\u0027 -count=1\n```\n\nExpected attack observation:\n\n```text\nstatus=202 downstream_route=/{id} protected_id=public%2Fstatus authentication_calls=0\nwiring=Router.Use status=202 downstream_route=/{id} protected_id=public%2Fstatus authentication_calls=0\n```\n\nControls included in the test show that:\n\n- `/ordinary` selects the protected operation, invokes authentication once, and is\n  rejected with HTTP 401;\n- `/public/status` reaches only the intentionally public handler;\n- the encoded request reaches the protected `/{id}` handler with HTTP 202 while the\n  authentication callback remains uncalled;\n- both external wrapping and the documented\n  `router.Use(validationHandler.Middleware)` wiring reproduce the same result.\n\n## Reverse-proxy reachability\n\nThe same request was reproduced through Nginx 1.31.3 using the official\n`nginx:alpine` image digest\n`sha256:4a73073bd557c65b759505da037898b61f1be6cbcc3c2c3aeac22d2a470c1752`.\n\nThe exact container invocation was:\n\n```sh\ndocker run --rm --name kin-openapi-nginx \\\n  --add-host=host.docker.internal:host-gateway \\\n  -p 18081:8080 -p 18082:8081 \\\n  -v \"$PWD/poc/nginx.conf:/etc/nginx/nginx.conf:ro\" \\\n  nginx:alpine\n```\n\nContainer port 8080 uses `proxy_pass http://host.docker.internal:18080;` without a\nreplacement URI. Host port 18081 therefore preserved `/public%2Fstatus`; the protected\nhandler returned HTTP 202 and the\nauthentication callback remained at zero calls. With\n`proxy_pass http://host.docker.internal:18080/;` on container port 8081 / host port\n18082, Nginx canonicalized the upstream URI; both layers selected `/public/status` and\nthe bypass did not occur.\n\nNginx access-log observations:\n\n```text\nserver_port=8080 \"GET /public%2Fstatus HTTP/1.1\" 202 0 \"curl/8.7.1\"\nserver_port=8081 \"GET /public%2Fstatus HTTP/1.1\" 204 0 \"curl/8.7.1\"\nserver_port=8080 \"GET /ordinary HTTP/1.1\" 401 0 \"curl/8.7.1\"\n```\n\nThe response route headers were `X-Poc-Route: /{id}` on the preserving listener and\n`X-Poc-Route: /public/status` on the canonicalizing listener. Backend observations for\nthe two requests were:\n\n```text\nrequest_uri=\"/public%2Fstatus\" path=\"/public/status\" raw_path=\"/public%2Fstatus\" auth_before=0\ncompleted request_uri=\"/public%2Fstatus\" auth_after=0\nrequest_uri=\"/public/status\" path=\"/public/status\" raw_path=\"\" auth_before=0\ncompleted request_uri=\"/public/status\" auth_after=0\n```\n\nThis control shows that upstream path handling is a deployment precondition rather\nthan claiming that every proxy configuration is affected.\n\nThe canonical protected control produced:\n\n```text\nrequest_uri=\"/ordinary\" path=\"/ordinary\" raw_path=\"\" auth_before=0\ncompleted request_uri=\"/ordinary\" auth_after=1\n```\n\n## Suggested remediation\n\nThe authentication layer and downstream dispatcher must select the same OpenAPI\noperation from the same request representation.\n\nPotential approaches:\n\n1. make `ValidationHandler` accept a caller-supplied `routers.Router` and require it to\n   match downstream routing semantics;\n2. document that `NewValidator` already accepts a router but is safe only when the\n   supplied router selects operations using the same semantics as the dispatcher;\n   callers must also supply an `AuthenticationFunc` through `ValidationOptions`, or\n   protected requests fail with the existing missing-authentication-service error;\n3. as an interim hardening option, make `ValidationHandler` fail closed on an encoded\n   path separator when `URL.Path` and `URL.RawPath` can select different operations,\n   and verify this behavior against the full suite;\n4. document the route-identity requirement and add encoded-separator regression tests.\n\nReplacing the legacy router with the kin-openapi gorilla router closes this PoC, but a\nlocal compatibility check changed two existing missing-path-parameter tests from HTTP\n400 semantics to route-not-found HTTP 404 semantics. A direct router swap is therefore\nnot a fully validated drop-in fix.\n\n## Public-reference triage\n\nThe public advisory list and related path-encoding reports reviewed on 2026-08-18 did\nnot describe this authentication-boundary crossing. Relevant nearby reports include\nissues #397, #1089, and #1105 and PR #400. This search is not proof of novelty; please\ndeduplicate against private reports.\n\n## Credit\n\nPreferred credit: Satoru Kanno (GMO CONNECT Inc., GMO Internet Group, Inc.)",
  "id": "GHSA-23vg-4cjm-66q5",
  "modified": "2026-10-15T20:19:20Z",
  "published": "2026-10-15T20:19:20Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/getkin/kin-openapi/security/advisories/GHSA-23vg-4cjm-66q5"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-100351"
    },
    {
      "type": "WEB",
      "url": "https://github.com/getkin/kin-openapi/commit/eda80e2676e9f577ceed2dd80e64f16083edb041"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/getkin/kin-openapi"
    },
    {
      "type": "WEB",
      "url": "https://github.com/getkin/kin-openapi/releases/tag/v0.147.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "kin-openapi: ValidationHandler security-requirement bypass via encoded-path operation confusion"
}

Sightings

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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
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Action not permitted

CVE-2026-100351 (GCVE-0-2026-100351)

FKIE_CVE-2026-100351

GHSA-23VG-4CJM-66Q5

Summary

Affected products

Security impact

Root cause

Reproduction

Reverse-proxy reachability

Suggested remediation

Public-reference triage

Credit

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