Traefik v3.7.0 Authentication Bypass via from-to-www-redirect

Description

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.

Timeline

Scores

EPSS (exploitation in 30 days)

0.65% · top 49% of all CVEs (7 Nov 2026)

CISA SSVC

Exploitation: none · Automatable: yes · Technical impact: total

The list uses the assigner's score when there is one, then CISA's, then NVD's: Critical 9.3.

Weakness

• CWE-639: Authorization Bypass Through User-Controlled Key (opens in a new tab)All about CWE-639 and its CVEs

Affected products

• traefik · traefik

  • affected 3.7.0 – ≤ 3.7.13

References (2)

• GitHub Security Advisory (GHSA-cjr6-pf59-jq29) (opens in a new tab)vendor-advisory
• VulnCheck Advisory: Traefik v3.7.0 Authentication Bypass via from-to-www-redirect (opens in a new tab)third-party-advisory

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2026-88877](https://trackcve.app/badge/CVE-2026-88877.svg)](https://trackcve.app/cve/CVE-2026-88877)

Record last updated 8 Oct 2026, 15:51 UTC.