CVE-2025-66490

EPSS 0.02%

Path Normalization Bypass in Traefik Router + Middleware Rules

Published: 12/8/2025Modified: 4/16/2026

Description

## 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 ```yaml apiVersion: traefik.io/v1alpha1 kind: IngressRoute metadata: name: my-service spec: routes: - match: PathPrefix(‘/admin/’) kind: Rule services: - name: service-a port: 8080 middlewares: - name: my-security-middleware - match: PathPrefix(‘/’) kind: Rule services: - name: service-a port: 8080 ``` 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](https://github.com/traefik/traefik/issues). <details> <summary>Original Description</summary>### Summary A vulnerability exists in Traefik’s path matching logic that allows attackers to bypass access-control middleware (e.g., blocking rules) by using URL-encoded paths. I found this vulnerability while playing PwnSec CTF 2025 with my team @0xL4ugh ### Details Traefik evaluates router rules before decoding or normalizing the request path, but forwards the request after decoding to the backend service. As a result, routes meant to block access to sensitive endpoints (such as internal, beta, or admin endpoints) can be trivially bypassed. ### PoC Traefik configuration used in this issue : ```[http.routers.flask-router-report-deny] entryPoints = ["web"] rule = "PathPrefix(`/report_note`)" priority = 10 middlewares = ["block-access"] service = "flask-service" [http.middlewares.block-access.replacePathRegex] regex = ".*" replacement = "/blocked" ``` The intention is to block all access to /report_note. However, the following request bypasses the block: ``` POST /%2freport_note HTTP/1.1 Host: localhost:62814 ``` ### Impact Access Control Bypass: Any endpoint intended to be blocked (e.g., admin/debug/beta APIs) can be accessed by URL-encoding slashes or other characters. This could lead to: - Unauthorized access to restricted endpoints - Execution of protected internal functionality - Potential privilege escalation - Bypass of security policies enforced via Traefik routing rules </details>

Affected packages (6)

CVSS scores

SourceVersionSeverityVector
osvCVSS 4.0—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

References (5)