# 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.

- **Severity:** Medium 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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 9 Dec 2025
- **Updated:** 9 Dec 2025
- **Also known as:** CLEANSTART-2026-PP49330, GHSA-gm3x-23wp-hc2c, GO-2025-4206, MINI-2328-c8qx-6xr6, MINI-6cw8-c23j-vvcj

## 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 (Interpretation Conflict)

## 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 | Ecosystem | 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 |
| `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: Traefik Traefik.

## How do I fix CVE-2025-66490?

Upgrade to a fixed version.

## 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](https://insights.sbomify.com/CVE-2024-45410/): HTTP client can remove the X-Forwarded headers in Traefik (critical 9.8)
- [CVE-2026-88877](https://insights.sbomify.com/CVE-2026-88877/): Traefik v3.7.0 Authentication Bypass via from-to-www-redirect (critical 9.3)
- [CVE-2026-85595](https://insights.sbomify.com/CVE-2026-85595/): Traefik before v2.11.55 and v3.0.0 through v3.7.10 Authentication Bypass via digestAuth (critical 9.3)
- [CVE-2026-88007](https://insights.sbomify.com/CVE-2026-88007/): Traefik HTTP/3 Backend NTLM Connection Reuse (critical 9.1)
- [CVE-2026-88009](https://insights.sbomify.com/CVE-2026-88009/): Traefik: Rootless HTTP/1 request-target routes as "/" but is forwarded verbatim, bypassing path-scoped routing, middleware guards and access logging (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-66490 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-66490 exists.

Affected packages and fixed versions:
- github.com/traefik/traefik (Go): affected all versions; no fix listed
- github.com/traefik/traefik (Go): affected all versions up to 1.7.34; no fix listed
- github.com/traefik/traefik (Go): affected all versions up to 1.7.34; no fix listed
- github.com/traefik/traefik/v2 (Go): affected all versions; fixed in 2.11.32
- github.com/traefik/traefik/v2 (Go): affected all versions; fixed in 2.11.32
- github.com/traefik/traefik/v2 (Go): affected all versions; fixed in 2.11.32
- github.com/traefik/traefik/v3 (Go): affected all versions; fixed in 3.6.3
- github.com/traefik/traefik/v3 (Go): affected all versions; fixed in 3.6.3
- github.com/traefik/traefik/v3 (Go): affected all versions; fixed in 3.6.3

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-66490/ (Markdown: https://insights.sbomify.com/CVE-2025-66490/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-66490
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-66490
- OSV: https://osv.dev/vulnerability/CVE-2025-66490

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-66490/
Summaries are generated and may contain mistakes; the official description above is the record.