Bug 2512295 (CVE-2026-71326)

Summary: CVE-2026-71326 github.com/traefik/traefik: Traefik: Authenticated identity spoofing via BasicAuth key collision
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
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Priority: low    
Version: unspecifiedCC: sdawley
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Traefik. The BasicAuth middleware in Traefik reuses a key for concurrent password checks, which is generated by concatenating the password and secret without a delimiter. An attacker with a valid credential and the corresponding stored hash can exploit this vulnerability to authenticate as an unconfigured username. This identity spoofing is possible when the 'headerField' is configured to trust forwarded identity information.
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Description OSIDB Bzimport 2026-08-06 22:27:50 UTC 
Traefik is an open source HTTP reverse proxy and load balancer. From 3.6.11 until 3.6.25 and 3.7.10, Traefik's BasicAuth middleware in pkg/middlewares/auth/basic_auth.go deduplicates concurrent password checks with a singleflight key built from the delimiter-free concatenation of password and secret, allowing an attacker who has a valid credential and the stored hash to authenticate as an unconfigured username when headerField trusts the forwarded identity. This issue is fixed in 3.6.25 and 3.7.10.