What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 8.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-03-27 · updated 2026-07-15
• Weakness: CWE-290

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 products

• Traefik: before 2.11.42; from 3.0.0 before 3.6.12; 3.7.0-ea1, 3.7.0-ea2 — fixed in 2.11.42, 3.6.12

How to fix

Upgrade to a fixed version: Traefik 2.11.42, 3.6.12. Check the vendor advisory for mitigations.

References

• https://github.com/traefik/traefik/releases/tag/v2.11.42
• https://github.com/traefik/traefik/releases/tag/v3.6.11
• https://github.com/traefik/traefik/releases/tag/v3.7.0-ea.3
• https://github.com/traefik/traefik/security/advisories/GHSA-qr99-7898-vr7c
• https://access.redhat.com/errata/RHSA-2026:10175
• https://access.redhat.com/security/cve/CVE-2026-33433
• https://bugzilla.redhat.com/show_bug.cgi?id=2452289
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33433.json

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