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9.3
CVE-2026-88877: Traefik 3.7 permits unauthenticated access via redirect
CVE-2026-88877 · published 1 month ago
Summary
Traefik versions 3.7.0 through 3.7.11 can bypass login checks when a specific redirect setting is used together with authentication. This lets users reach protected services without the required credentials or IP restrictions. Upgrade to version 3.7.12 or later to close the gap.
What to do
The CVE record does not list a fixed version. Check the vendor's site or the advisory links below - a fix may already be released.
Affected software
| Vendor | Product | Affected versions |
|---|---|---|
| traefik | traefik |
<= 3.7.13 >= 3.7.0, < 3.7.12 |
Original advisory text
Traefik v3.7.0 Authentication Bypass via from-to-www-redirect
Traefik is a HTTP reverse proxy and load balancer. In versions >= v3.7.0 and <= v3.7.11, the Kubernetes ingress-nginx provider mishandles Ingresses that carry both an authentication annotation and the nginx.ingress.kubernetes.io/from-to-www-redirect annotation. For such Ingresses the provider creates an additional 'sibling' router that matches on the host alone, carries only the RedirectRegex middleware, and still points at the parent router's protected backend service. Because RedirectRegex is not a terminal handler, a request its pattern does not match is forwarded to the backend, and because the redirect pattern only accepts a numeric port while Traefik's host matcher canonicalizes the authority via net.SplitHostPort, a request with a non-numeric or empty port (for example 'Host: www.example.com:x') selects the sibling router, misses the redirect, and is proxied to the protected backend with none of the Ingress's annotation-derived middlewares applied. This discards not only authentication (e.g. BasicAuth) but every annotation-derived middleware, including source-IP allowlisting. Traefik v2 and v3 releases before v3.7.0 are not affected. The issue is fixed in v3.7.12.
References
- https://nvd.nist.gov/vuln/detail/CVE-2026-88877 Vendor Advisory
- https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/88xxx/CVE-2026-88877... Vendor Advisory
- https://github.com/traefik/traefik/security/advisories/GHSA-cjr6-pf59-jq29 Patch Vendor Advisory
- https://www.vulncheck.com/advisories/traefik-3.7.0-authentication-bypass-via-fro... Third Party Advisory
Internet-facing
3 days
Internal
60 days
- Not known to be exploited
- Can be exploited automatically
- Gives an attacker full control
Severity
9.3
Critical
Type
CWE-639Authorization Bypass Through User-Controlled Key
Timeline
Published10 Sep 2026
Updated14 Oct 2026
First seen10 Sep 2026
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