Traefik up to 2.11.42/3.6.13/3.7.0-rc.1 StripPrefixRegex Middleware name resolution

Summaryinfo

A vulnerability was found in Traefik up to 2.11.42/3.6.13/3.7.0-rc.1. It has been classified as critical. This affects an unknown function of the component StripPrefixRegex Middleware. This manipulation causes name resolution. The identification of this vulnerability is CVE-2026-40912. It is possible to initiate the attack remotely. There is no exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability classified as critical was found in Traefik up to 2.11.42/3.6.13/3.7.0-rc.1. Affected by this vulnerability is an unknown code block of the component StripPrefixRegex Middleware. The manipulation with an unknown input leads to a name resolution vulnerability. The CWE definition for the vulnerability is CWE-706. The product uses a name or reference to access a resource, but the name/reference resolves to a resource that is outside of the intended control sphere. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.43, 3.6.14, and 3.7.0-rc.2, there is a high severity authentication bypass vulnerability in Traefik's StripPrefixRegex middleware when used in combination with ForwardAuth, BasicAuth, or DigestAuth. The middleware matches the regex against the decoded URL path but uses the resulting byte length to slice the percent-encoded raw path. When a dot (or multiple dots) appears in the prefix portion of the URL, the raw path after stripping becomes a dot-segment (e.g. /./admin/secret). ForwardAuth receives this dot-segment path in X-Forwarded-Uri, which does not match the protected path patterns and therefore allows the request through. The backend then normalizes the dot-segment to the real path per RFC 3986 and serves the protected content An unauthenticated attacker can exploit this against any backend that performs dot-segment normalization. This issue has been patched in versions 2.11.43, 3.6.14, and 3.7.0-rc.2.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-40912 since 04/15/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. The technical details are unknown and an exploit is not publicly available.

The vulnerability scanner Nessus provides a plugin with the ID 311474 (Traefik < 2.11.43 / 3.x < 3.6.14 Multiple Vulnerabilities), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 2.11.43, 3.6.14 or 3.7.0-rc.2 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at Tenable (311474). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

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
• 2.11.42
• 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
• 3.6.11
• 3.6.12
• 3.6.13
• 3.7.0-rc.0
• 3.7.0-rc.1

Website

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

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Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

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