CVE-2026-35051: Traefik auth bypass in ForwardAuth middleware via header spoofing

CVE-2026-35051 · Severity: critical · CVSS 10 · Published 2026-04-30

Traefik, a popular tool used to manage and route web traffic, contains a security flaw that could allow unauthorized users to bypass login requirements. When Traefik is set up behind another proxy server, an attacker can send specially crafted web requests that trick the system into granting access to protected areas. This could lead to the exposure of sensitive customer data or unauthorized control over internal business applications.

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-2026-35051 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-35051 being exploited in the wild.
How severe is CVE-2026-35051?
Critical severity, with a CVSS score of 10, published 30 April 2026.
Which products and versions are affected?
github.com/traefik/traefik (Go) SEMVER:introduced=0, SEMVER:introduced=0,last_affected=1.7.34; github.com/traefik/traefik/v2 (Go) SEMVER:introduced=0,fixed=2.11.43; github.com/traefik/traefik/v3 (Go) SEMVER:introduced=3.0.0-beta1,fixed=3.6.14,introduced=3.7.0-ea.1,fixed=3.7.0-rc.2, SEMVER:introduced=3.7.0-ea.1,fixed=3.7.0-rc.2.
Is there a fix for CVE-2026-35051?
Yes. github.com/traefik/traefik/v2 (Go): upgrade to 2.11.43 or later; github.com/traefik/traefik/v3 (Go): upgrade to 3.7.0-rc.2 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-35051 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-35051?
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/v2 (Go): upgrade to 2.11.43 or later
    go get github.com/traefik/traefik/v2@v2.11.43
  • github.com/traefik/traefik/v3 (Go): upgrade to 3.7.0-rc.2 or later
    go get github.com/traefik/traefik/v3@v3.7.0-rc.2

Technical details

An authentication bypass vulnerability exists in Traefik's ForwardAuth middleware due to insufficient verification of data authenticity. When Traefik is configured with 'trustForwardHeader=false' and deployed behind a trusted upstream proxy, the middleware fails to strip or rebuild the 'X-Forwarded-Prefix' header before sending subrequests to the authentication service. While other 'X-Forwarded-*' headers are correctly handled, the 'X-Forwarded-Prefix' remains attacker-controlled. If the downstream authentication service relies on this header to make authorization or routing decisions, a remote, unauthenticated attacker can spoof the prefix to bypass access controls. The issue is patched in versions 2.11.43, 3.6.14, and 3.7.0-rc.2.

Affected products

  • Traefik Labs Traefik < 2.11.43, >= 3.0.0-beta1 < 3.6.14, >= 3.7.0-ea.1 < 3.7.0-rc.2
  • Red Hat Red Hat OpenShift Dev Spaces 3.28 3.28

Identifiers

  • CVE-2026-35051
  • GHSA-6384-m2mw-rf54
  • GO-2026-5163

Timeline

  • 2026-04-22: patched: Fixed versions 2.11.43, 3.6.14, and 3.7.0-rc.2 released
  • 2026-04-24: advisory: GitHub Security Advisory GHSA-6384-m2mw-rf54 published
  • 2026-04-30: disclosed: CVE-2026-35051 published to NVD

References

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