Summary
Example
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.
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 = ".*"
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
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.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
Frequently Asked Questions
- What is CVE-2025-66490? CVE-2025-66490 is a medium-severity security vulnerability in github.com/traefik/traefik (go), affecting versions <= 1.7.34. It is fixed in 2.11.32, 3.6.3.
- Which packages are affected by CVE-2025-66490?
github.com/traefik/traefik(go) (versions <= 1.7.34)github.com/traefik/traefik/v2(go) (versions < 2.11.32)github.com/traefik/traefik/v3(go) (versions < 3.6.3)
- Is there a fix for CVE-2025-66490? Yes. CVE-2025-66490 is fixed in 2.11.32, 3.6.3. Upgrade to this version or later.
- Is CVE-2025-66490 exploitable, and should I be worried? Whether CVE-2025-66490 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2025-66490 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2025-66490?
- Upgrade
github.com/traefik/traefik/v2to 2.11.32 or later - Upgrade
github.com/traefik/traefik/v3to 3.6.3 or later
- Upgrade