Path Normalization Bypass in Traefik Router + Middleware Rules

Exploitation

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

CVSS 4.0

6.9 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N · score source

EPSS

• CVE-2025-66490: 0.44% estimated exploitation activity in the next 30 days; percentile 38.23 (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.

Impact There is a potential vulnerability in Traefik managing the requests using a PathPrefix, Path or PathRegex matcher. When Traefik is configured to route the requests to a backend using a matcher based on the path; if the request path contains an encoded restricted character from the following set ('/', '\', 'Null', ';', '?', '#'), it’s possible to target a backend, exposed using another router, by-passing the middlewares chain. Example In such a case, the request http://mydomain.example.com/admin%2F will reach the backend service-a without operating the middleware my-security-middleware and passing the security put in place for the /admin/ path. Patches - https://github.com/traefik/traefik/releases/tag/v2.11.32 - https://github.com/traefik/traefik/releases/tag/v3.6.4 For more information If you have any questions or comments about this advisory, please open an issue. <details <summaryOriginal Description</summary

Summary A vulnerability exists in Traefik’s path matching logic…

Published by the source

8 Dec 2025, 16:42 UTC

Last modified by the source

17 Dec 2025, 00:44 UTC

Source last checked

26 Oct 2026, 15:13 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-gm3x-23wp-hc2c

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# Patch Next advisory brief: CVE-2025-66490

Advisory: Path Normalization Bypass in Traefik Router + Middleware Rules
IDs: CVE-2025-66490, GHSA-gm3x-23wp-hc2c
Record: https://patchnext.com/advisories/cve-2025-66490 (revision 1, source checked 26 Oct 2026, 15:13 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Partial vendor fix; fixed versions by package: github.com/traefik/traefik/v3 3.6.3; github.com/traefik/traefik/v2 2.11.32. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/traefik/traefik/v3: affected < 3.6.3; fixed in 3.6.3
- Go github.com/traefik/traefik/v2: affected < 2.11.32; fixed in 2.11.32
- Go github.com/traefik/traefik: affected <= 1.7.34

## Suggested inspection (read-only)
- Go github.com/traefik/traefik/v3: check the installed version with your package manager.
- Go github.com/traefik/traefik/v2: check the installed version with your package manager.
- Go github.com/traefik/traefik: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/traefik/traefik/v3, github.com/traefik/traefik/v2, github.com/traefik/traefik.
- 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://github.com/advisories/GHSA-gm3x-23wp-hc2c (GitHub-reviewed advisory GHSA-gm3x-23wp-hc2c lists affected ranges: Go github.com/traefik/traefik >=0 =0 =0 <3.6.3)

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