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

Severity: high (CVSS 8.2 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.8% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-04-30 · updated 2026-07-15
Weakness: CWE-706

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.

Affected products

Traefik: before 2.11.43; from 3.0.0 before 3.6.14; 3.7.0-ea1, 3.7.0-ea2, 3.7.0-ea3, 3.7.0-rc1 — fixed in 2.11.43, 3.6.14

How to fix

Upgrade to a fixed version: Traefik 2.11.43, 3.6.14. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-40912 or the next vulnerability affects your stack