CVE-2026-35051

Traefik's ForwardAuth trustForwardHeader=false allows spoofed X-Forwarded-Prefix to bypass authentication

This is an authentication bypass / trust-boundary bypass.

Affected deployments are those that:

• run Traefik behind a trusted upstream proxy
• use ForwardAuth
• rely on trustForwardHeader=false to avoid trusting client-supplied forwarded headers
• pass X-Forwarded-Prefix to the auth service, which happens by default when authRequestHeaders is empty
• make authorization or routing decisions based on X-Forwarded-Prefix, especially when StripPrefix runs before ForwardAuth
  In those environments, an unauthenticated external attacker can influence the auth service's view of the protected path and gain access to backend routes that should be denied.

CVE-2026-35051 has a CVSS score of 10.0 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.7.0-rc.2, 3.6.14, 2.11.43); upgrading removes the vulnerable code path.

Kodem intelligence

• https://github.com/traefik/traefik/releases/tag/v2.11.43
• https://github.com/traefik/traefik/releases/tag/v3.6.14
• https://github.com/traefik/traefik/releases/tag/v3.7.0-rc.2

1. What is CVE-2026-35051? CVE-2026-35051 is a high-severity security vulnerability in github.com/traefik/traefik/v3 (go), affecting versions >= 3.7.0-ea.1, < 3.7.0-rc.2. It is fixed in 3.7.0-rc.2, 3.6.14, 2.11.43.
2. How severe is CVE-2026-35051? CVE-2026-35051 has a CVSS score of 10.0 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2026-35051?
   • github.com/traefik/traefik/v3 (go) (versions >= 3.7.0-ea.1, < 3.7.0-rc.2)
   • github.com/traefik/traefik/v2 (go) (versions < 2.11.43)
   • github.com/traefik/traefik (go) (versions <= 1.7.34)
4. Is there a fix for CVE-2026-35051? Yes. CVE-2026-35051 is fixed in 3.7.0-rc.2, 3.6.14, 2.11.43. Upgrade to this version or later.
5. Is CVE-2026-35051 exploitable, and should I be worried? Whether CVE-2026-35051 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
6. What actually determines whether CVE-2026-35051 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.
7. How do I fix CVE-2026-35051?
   • Upgrade github.com/traefik/traefik/v3 to 3.7.0-rc.2 or later
   • Upgrade github.com/traefik/traefik/v3 to 3.6.14 or later
   • Upgrade github.com/traefik/traefik/v2 to 2.11.43 or later