CVE-2026-33433
Last modified
CVE-2026-33433 is a high-severity vulnerability rated 8.8/10 on the CVSS scale. 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. EPSS estimates a 0.47% chance of exploitation in the next 30 days.
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.
Metrics
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Weakness Enumeration
Affected Software
| Vendor | Product | Versions | Update |
|---|---|---|---|
| Traefik | Traefik | < 2.11.42 | — |
| Traefik | Traefik | >= 3.0.0, < 3.6.12 | — |
| Traefik | Traefik | 3.7.0 | Ea1 |
References
- https://github.com/traefik/traefik/releases/tag/v2.11.42Product, Release Notes
- https://github.com/traefik/traefik/releases/tag/v3.6.11Product, Release Notes
- https://github.com/traefik/traefik/releases/tag/v3.7.0-ea.3Product, Release Notes
- https://github.com/traefik/traefik/security/advisories/GHSA-qr99-7898-vr7cExploit, Patch, Vendor Advisory
Timeline
- Published
- Last Modified
- Status
- Modified
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