CVE-2026-33433 Traefik Vulnerable to BasicAuth/DigestAuth Identity Spoofing via Non-Canonical headerField
An authenticated attacker can impersonate any identity to the backend by exploiting non-canonical header field configurations in Traefik.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-33433?
CVE-2026-33433 is a medium-severity authentication bypass vulnerability in Traefik Traefik, published on 27 Mar 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Official 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.
Weakness: CWE-290
Which versions are affected by CVE-2026-33433?
9 open source packages ship an affected version, including github.com/traefik/traefik/v3, github.com/traefik/traefik and github.com/traefik/traefik/v2. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/traefik/traefik/v3 Go | From 3.0.0-beta1 | 3.6.12, 3.7.0-ea.3 |
github.com/traefik/traefik/v3 Go | From 3.0.0-beta1 | 3.6.12 |
github.com/traefik/traefik/v3 Go | From 3.0.0-beta1 | 3.6.12 |
github.com/traefik/traefik/v3 Go | From 3.7.0-ea.1 | 3.7.0-ea.3 |
github.com/traefik/traefik/v3 Go | From 3.7.0-ea.1 | 3.7.0-ea.3 |
github.com/traefik/traefik Go | All versions | None |
3 more packages
github.com/traefik/traefik/v2 Go | All versions | 2.11.42 |
github.com/traefik/traefik/v2 Go | All versions | 2.11.42 |
github.com/traefik/traefik/v2 Go | All versions | 2.11.42 |
Products include Traefik Traefik.
How do I fix CVE-2026-33433?
Upgrade github.com/traefik/traefik/v3 to a fixed version for your release line: 3.6.12 or 3.7.0-ea.3.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-33433 being exploited?
There is no known exploitation of CVE-2026-33433 in the wild and no public exploit code.
Other vulnerabilities in Traefik Traefik
- CVE-2024-45410 HTTP client can remove the X-Forwarded headers in Traefik
- CVE-2026-88877 Traefik v3.7.0 Authentication Bypass via from-to-www-redirect
- CVE-2026-85595 Traefik before v2.11.55 and v3.0.0 through v3.7.10 Authentication Bypass via digestAuth
- CVE-2026-88007 Traefik HTTP/3 Backend NTLM Connection Reuse
- CVE-2026-88009 Traefik: Rootless HTTP/1 request-target routes as "/" but is forwarded verbatim, bypassing path-scoped routing, middleware guards and access logging
Sources
Also known as CLEANSTART-2026-SB40990, ECHO-f91f-26ea-bbf3, GHSA-qr99-7898-vr7c, GO-2026-4893, MINI-8xqp-fgcv-vmrf, MINI-hf3c-p65f-r4ch and 1 more.