CVE-2026-33433: Traefik Vulnerable to BasicAuth/DigestAuth Identity Spoofing via Non-Canonical headerField

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 vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Attack vector

Network

Complexity

Low

Privileges

Low

User interaction

None

Confidentiality

High

Integrity

High

Availability

High

Scope

Unchanged

Exploitation

Is it being used?

Exploit prediction (EPSS)0.5% · higher than 42% of CVEs

Exploited in the wildNo evidence yet

CISA KEVNot listed

Ransomware campaign useNot known

Affected products

Which versions

TR

traefik · traefik

< 2.11.42; >= 3.0.0-beta1, < 3.6.11; >= 3.7.0-ea.1, < 3.7.0-ea.3 · source: vendor, NVD

RH

Red Hat OpenShift Dev Spaces 3.27 · Red Hat

All versions, or not specified · source: CISA