Traefik: StripPrefixRegex auth bypass via Path/RawPath desync_CVE-2026-40912

7.8 / 10

HIGH

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:L/SA:N

Description

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.

Basic Information

ID CVE-2026-40912

Source GitHub_M

Published Apr 30, 2026 at 20:38

Affected Product

Vendor traefik

Product traefik

Version < 2.11.43

Affected Versions traefik traefik < 2.11.43
traefik traefik >= 3.0.0-beta1, < 3.6.14
traefik traefik >= 3.7.0-ea.1, < 3.7.0-rc.2

CWE Classification

CWE-706

References

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