CVE-2025-66490 Traefik doesn't Prevent Path Normalization Bypass in Router + Middleware Rules
Attackers can bypass security middleware and reach unintended backends by using URL-encoded characters in path-based routing rules.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-66490?
CVE-2025-66490 is a medium-severity path traversal vulnerability in Traefik Traefik, published on 9 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-436
Which versions are affected by CVE-2025-66490?
9 open source packages ship an affected version, including github.com/traefik/traefik, github.com/traefik/traefik/v2 and github.com/traefik/traefik/v3. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/traefik/traefik Go | All versions | None |
github.com/traefik/traefik Go | All versions to 1.7.34 | None |
github.com/traefik/traefik Go | All versions to 1.7.34 | None |
github.com/traefik/traefik/v2 Go | All versions | 2.11.32 |
github.com/traefik/traefik/v2 Go | All versions | 2.11.32 |
github.com/traefik/traefik/v2 Go | All versions | 2.11.32 |
3 more packages
github.com/traefik/traefik/v3 Go | All versions | 3.6.3 |
github.com/traefik/traefik/v3 Go | All versions | 3.6.3 |
github.com/traefik/traefik/v3 Go | All versions | 3.6.3 |
Products include Traefik Traefik.
How do I fix CVE-2025-66490?
Upgrade to a fixed version.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2025-66490 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-66490 exists.
Other vulnerabilities in Traefik Traefik
- CVE-2024-45410 HTTP client can remove the X-Forwarded headers in Traefik
- CVE-2026-88877 Traefik v3.7.0 Authentication Bypass via from-to-www-redirect
- CVE-2026-85595 Traefik before v2.11.55 and v3.0.0 through v3.7.10 Authentication Bypass via digestAuth
- CVE-2026-88007 Traefik HTTP/3 Backend NTLM Connection Reuse
- CVE-2026-88009 Traefik: Rootless HTTP/1 request-target routes as "/" but is forwarded verbatim, bypassing path-scoped routing, middleware guards and access logging
Sources
Also known as CLEANSTART-2026-PP49330, GHSA-gm3x-23wp-hc2c, GO-2025-4206, MINI-2328-c8qx-6xr6, MINI-6cw8-c23j-vvcj.