kin-openapi: Unauthenticated panic (DoS) in openapi3filter legacy router via non-canonical/unsupported HTTP method on a static path

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-100347: 0.52% estimated exploitation activity in the next 30 days; percentile 43.92 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The openapi3filter.ValidationHandler (the exported, documented request-validation middleware) hard-wires the legacy router (routers/legacy). That router matches the incoming request method verbatim against a trie built exclusively from upper-cased canonical HTTP methods. A request carrying a method token that is not one of the 9 standard methods — a legitimate-but-unsupported token such as PROPFIND, or a non-canonical case variant such as lowercase get — misses the trie, leaves route == nil, and for an existing static path falls through to PathItem.GetOperation(method), whose default: case calls panic(...). The panic fires inside route resolution, before any authentication runs. This is an unauthenticated, remotely triggerable denial of service (recovered per-connection panic + unbounded error-log growth). Root Cause - openapi3filter/validationhandler.go:39 — ValidationHandler.Load() always constructs legacyrouter.NewRouter(doc); there is no alternative router option on this…

Published by the source

15 Oct 2026, 20:15 UTC

Last modified by the source

15 Oct 2026, 20:30 UTC

Source last checked

26 Oct 2026, 15:32 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-fh4f-47mf-f2gj

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-fh4f-47mf-f2gj

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# Patch Next advisory brief: CVE-2026-100347

Advisory: kin-openapi: Unauthenticated panic (DoS) in openapi3filter legacy router via non-canonical/unsupported HTTP method on a static path
IDs: CVE-2026-100347, GHSA-fh4f-47mf-f2gj
Record: https://patchnext.com/advisories/cve-2026-100347 (revision 2, source checked 26 Oct 2026, 15:32 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/getkin/kin-openapi 0.145.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/getkin/kin-openapi: affected <= 0.144.0; fixed in 0.145.0

## Suggested inspection (read-only)
- Go github.com/getkin/kin-openapi: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/getkin/kin-openapi.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-fh4f-47mf-f2gj (OSV record GHSA-fh4f-47mf-f2gj lists affected ranges: Go github.com/getkin/kin-openapi >=0 <0.145.0 (fixed))
- Verified: https://github.com/advisories/GHSA-fh4f-47mf-f2gj (GitHub-reviewed advisory GHSA-fh4f-47mf-f2gj lists affected ranges: Go github.com/getkin/kin-openapi >=0 <=0.144.0)

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