High severity8.8NVD Advisory· Published Mar 27, 2026· Updated Apr 3, 2026
CVE-2026-33433
CVE-2026-33433
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.
Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
github.com/traefik/traefik/v2Go | < 2.11.42 | 2.11.42 |
github.com/traefik/traefik/v3Go | >= 3.0.0-beta1, < 3.6.12 | 3.6.12 |
github.com/traefik/traefik/v3Go | >= 3.7.0-ea.1, < 3.7.0-ea.3 | 3.7.0-ea.3 |
Affected products
3Patches
0No patches discovered yet.
Vulnerability mechanics
AI mechanics synthesis has not run for this CVE yet.
References
6- github.com/traefik/traefik/security/advisories/GHSA-qr99-7898-vr7cnvdExploitPatchVendor AdvisoryWEB
- github.com/advisories/GHSA-qr99-7898-vr7cghsaADVISORY
- nvd.nist.gov/vuln/detail/CVE-2026-33433ghsaADVISORY
- github.com/traefik/traefik/releases/tag/v2.11.42nvdProductRelease NotesWEB
- github.com/traefik/traefik/releases/tag/v3.6.11nvdProductRelease NotesWEB
- github.com/traefik/traefik/releases/tag/v3.7.0-ea.3nvdProductRelease NotesWEB
News mentions
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