How severe is CVE-2025-66490?

No CVSS score has been assigned to CVE-2025-66490 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2025-66490?

CVE-2025-66490 affects the following packages: github.com/traefik/traefik (Go), github.com/traefik/traefik/v2 (Go), github.com/traefik/traefik/v3 (Go). Ecosystems affected: Go.

How do I fix CVE-2025-66490?

No patched version of github.com/traefik/traefik has shipped for CVE-2025-66490 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.

How do I detect CVE-2025-66490 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/traefik/traefik. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

How do I mitigate CVE-2025-66490 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2025-66490?

O3 pinpoints whether CVE-2025-66490 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is CVE-2025-66490 actively exploited in the wild?

No public exploit code has been indexed for CVE-2025-66490 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What type of vulnerability is CVE-2025-66490?

CVE-2025-66490 is classified as CWE-436 (CWE-436). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2025-66490 published, and has it been updated?

CVE-2025-66490 was published on December 9, 2025 and was last updated on August 5, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹 Go

CVE-2025-66490

CVE-2025-66490 is a CWE-436 vulnerability in github.com/traefik/traefik. O3 Security confirms whether CVE-2025-66490 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.

Traefik doesn't Prevent Path Normalization Bypass in Router + Middleware Rules

Also known asGHSA-gm3x-23wp-hc2cGO-2025-4206

Published

Dec 9, 2025

Updated

Aug 5, 2026

Affected

3 pkgs

Patched

2 / 3

Exploits

None indexed

Real-World Exposure

3 pkgs affected

🐹github.com/traefik/traefik🐹github.com/traefik/traefik/v2🐹github.com/traefik/traefik/v3

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

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.

Affected Packages

3 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/traefik/traefik`	all versions	No fix
🐹Go	`github.com/traefik/traefik/v2`	all versions	2.11.32
🐹Go	`github.com/traefik/traefik/v3`	all versions	3.6.3

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/traefik/traefik. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
No patched version of github.com/traefik/traefik has shipped for CVE-2025-66490 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2025-66490 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2025-66490. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

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.

O3 Security · Impact-Aware SCA

Is CVE-2025-66490 in your dependencies?

O3 detects CVE-2025-66490 across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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