Vulnerability Description
Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.42, 3.6.11, and 3.7.0-ea.3, when `headerField` is configured with a non-canonical HTTP header name (e.g., `x-auth-user` instead of `X-Auth-User`), an authenticated attacker can inject their own canonical version of that header to impersonate any identity to the backend. The backend receives two header entries — the attacker-injected canonical one is read first, overriding Traefik's non-canonical write. Versions 2.11.42, 3.6.11, and 3.7.0-ea.3 patch the issue.
CVSS Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Traefik | Traefik | < 2.11.42 |
Related Weaknesses (CWE)
References
- https://github.com/traefik/traefik/releases/tag/v2.11.42ProductRelease Notes
- https://github.com/traefik/traefik/releases/tag/v3.6.11ProductRelease Notes
- https://github.com/traefik/traefik/releases/tag/v3.7.0-ea.3ProductRelease Notes
- https://github.com/traefik/traefik/security/advisories/GHSA-qr99-7898-vr7cExploitPatchVendor Advisory
FAQ
What is CVE-2026-33433?
CVE-2026-33433 is a vulnerability with a CVSS score of 8.8 (HIGH). Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.42, 3.6.11, and 3.7.0-ea.3, when `headerField` is configured with a non-canonical HTTP header name (e.g., `x-auth-user` inste...
How severe is CVE-2026-33433?
CVE-2026-33433 has been rated HIGH with a CVSS base score of 8.8/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-33433?
Check the references section above for vendor advisories and patch information. Affected products include: Traefik Traefik.