CVE-2026-71326: Traefik BasicAuth identity spoofing via singleflight key collision

CVE-2026-71326 · Severity: medium · CVSS 4 · Published 2026-08-06

Traefik is a popular open-source edge router and load balancer used to manage web traffic. A flaw in its basic authentication system allows a user who already has valid credentials and access to the system's internal configuration to impersonate other users. This could allow an attacker to perform actions or access data belonging to a different account, potentially leading to unauthorized administrative changes or data exposure.

Technologies: github.com/traefik/traefik (Go), github.com/traefik/traefik/v2 (Go), github.com/traefik/traefik/v3 (Go), Traefik Labs Traefik Proxy. Vendors: Go, Traefik Labs.

Quick answers

Is CVE-2026-71326 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-71326 being exploited in the wild.
How severe is CVE-2026-71326?
Medium severity, with a CVSS score of 4, published 6 August 2026.
Which products and versions are affected?
github.com/traefik/traefik (Go) SEMVER:introduced=0; github.com/traefik/traefik/v2 (Go) SEMVER:introduced=0; github.com/traefik/traefik/v3 (Go) SEMVER:introduced=3.6.11,fixed=3.6.25, SEMVER:introduced=3.6.11,fixed=3.6.25,introduced=3.7.0,fixed=3.7.10.
Is there a fix for CVE-2026-71326?
Yes. github.com/traefik/traefik/v3 (Go): upgrade to 3.6.25, 3.7.10 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-71326 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-71326?
Check whether you run github.com/traefik/traefik (Go), github.com/traefik/traefik/v2 (Go), github.com/traefik/traefik/v3 (Go) or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • github.com/traefik/traefik/v3 (Go): upgrade to 3.6.25, 3.7.10 or later
    go get github.com/traefik/traefik/v3@v3.7.10

Technical details

A vulnerability exists in Traefik's BasicAuth middleware where concurrent password verifications are deduplicated using a 'singleflight' group. The deduplication key is formed by the delimiter-free concatenation of the submitted password and the stored secret (hash). An attacker who knows a valid password 'P' and its corresponding hash 'H' can submit a request for an unconfigured username using 'P+H' as the password. Because the secret for an unconfigured user is an empty string, the resulting key ('P+H' + '') matches the key of a concurrent valid request ('P' + 'H'). If the valid request starts the calculation, the attacker's request receives the successful result and is forwarded to the backend with the attacker-specified username. This allows identity spoofing and privilege escalation, especially when Traefik is configured to forward the authenticated username via a header field. Patches are available in versions 3.6.25 and 3.7.10.

Affected products

  • Traefik Labs Traefik >= 3.6.11, <= 3.6.24
  • Traefik Labs Traefik >= 3.7.0, <= 3.7.9

Identifiers

  • CVE-2026-71326
  • GHSA-6765-c87h-8mrf
  • GO-2026-6204

Timeline

  • 2026-08-03: disclosed: Initial disclosure on GitHub Advisories
  • 2026-08-06: advisory: Updated advisory published

References

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