CVE-2026-33433
High
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.
SeverityHigh
CVSS8.8
Exploit probability—
Product
Traefik
PublishedMar 27, 2026
First seenMar 27, 2026
Weakness typeCWE-290CWE-290
How to fix
Update
- traefik traefik2.11.42, 3.6.12 or later
- github.com/traefik/traefik/v22.11.42 or later
- github.com/traefik/traefik/v33.6.12, 3.7.0-ea.3 or later
Vendor advisories
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| traefik traefik | v < 2.11.42, 3.0.0 ≤ v < 3.6.12, 3.7.0 | 2.11.42, 3.6.12 |
| github.com/traefik/traefik/v2Go | v < 2.11.42 | 2.11.42 |
| github.com/traefik/traefik/v3Go | 3.0.0-beta1 ≤ v < 3.6.12, 3.7.0-ea.1 ≤ v < 3.7.0-ea.3, 3.0.0-beta1 ≤ v < 3.6.11 | 3.6.12, 3.7.0-ea.3 |
| github.com/traefik/traefikGo | No range specified | — |
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