Lack of data validation In github.com/traefik/traefik/v3
Description
Path Normalization Bypass in Traefik Router + Middleware Rules
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
apiVersion: traefik.io/v1alpha1 kind: IngressRoute metadata: name: my-service spec: routes: - match: PathPrefix(‘/admin/’) kind: Rule...
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
For more information
If you have any questions or comments about this advisory, please open an issue.
Original Description
### 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 @0xL4ughDetails
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 :
entryPoints = ["web"] rule = "PathPrefix(`/report_note`)" priority = 10 middlewares = ["block-access"] service = "flask-service" [http.middlewares.block-access.replacePathRegex] regex = ".*"...
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
Mitigation
Update Impact
Minimal update. May introduce new vulnerabilities or breaking changes.
Ecosystem | Component | Affected version | Patched versions |
|---|---|---|---|
 go | 3.6.3 | ||
go | 2.11.32 | ||
go | 2.0.0-alpha1+incompatible |
Aliases
References