Summaryinfo

A vulnerability categorized as critical has been discovered in Traefik up to 2.11.41/3.6.10. This vulnerability affects unknown code. The manipulation results in authentication spoofing. This vulnerability was named CVE-2026-33433. The attack may be performed from remote. There is no available exploit. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, was found in Traefik up to 2.11.41/3.6.10. Affected is an unknown functionality. The manipulation with an unknown input leads to a authentication spoofing vulnerability. CWE is classifying the issue as CWE-290. This attack-focused weakness is caused by incorrectly implemented authentication schemes that are subject to spoofing attacks. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is traded as CVE-2026-33433 since 03/19/2026. The exploitability is told to be difficult. It is possible to launch the attack remotely. Additional levels of successful authentication are necessary for exploitation. There are neither technical details nor an exploit publicly available.

Upgrading to version 2.11.42, 3.6.11 or 3.7.0-ea.3 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-16616). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Name

• Traefik

Version

• 2.11.0
• 2.11.1
• 2.11.2
• 2.11.3
• 2.11.4
• 2.11.5
• 2.11.6
• 2.11.7
• 2.11.8
• 2.11.9
• 2.11.10
• 2.11.11
• 2.11.12
• 2.11.13
• 2.11.14
• 2.11.15
• 2.11.16
• 2.11.17
• 2.11.18
• 2.11.19
• 2.11.20
• 2.11.21
• 2.11.22
• 2.11.23
• 2.11.24
• 2.11.25
• 2.11.26
• 2.11.27
• 2.11.28
• 2.11.29
• 2.11.30
• 2.11.31
• 2.11.32
• 2.11.33
• 2.11.34
• 2.11.35
• 2.11.36
• 2.11.37
• 2.11.38
• 2.11.39
• 2.11.40
• 2.11.41
• 3.6.0
• 3.6.1
• 3.6.2
• 3.6.3
• 3.6.4
• 3.6.5
• 3.6.6
• 3.6.7
• 3.6.8
• 3.6.9
• 3.6.10

Website

• Product: https://github.com/traefik/traefik/

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