CVE-2026-33433

medium

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.

References

https://github.com/traefik/traefik/security/advisories/GHSA-qr99-7898-vr7c

https://github.com/traefik/traefik/releases/tag/v3.7.0-ea.3

https://github.com/traefik/traefik/releases/tag/v3.6.11

https://github.com/traefik/traefik/releases/tag/v2.11.42

Details

Source: Mitre, NVD

Published: 2026-03-27

Updated: 2026-03-27

Risk Information

CVSS v2

Base Score: 7.5

Vector: CVSS2#AV:N/AC:L/Au:N/C:P/I:P/A:P

Severity: High

CVSS v3

Base Score: 9.8

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Severity: Critical

CVSS v4

Base Score: 5.1

Vector: 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

Severity: Medium

EPSS

EPSS: 0.00011