Traefik Kubernetes CRD allows unauthorized cross-namespace middleware binding

Summary

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 potential vulnerability in Traefik's Kubernetes CRD provider cross-namespace isolation enforcement. When providers.kubernetesCRD.allowCrossNamespace=false, Traefik correctly rejects direct cross-namespace middleware references from IngressRoute objects, but fails to apply the same restriction to middleware references nested inside a Chain middleware's spec.chain.middlewares[]. An actor with permission to create or update Traefik CRDs in their own namespace can exploit this to cause Traefik to resolve and apply middleware objects from another namespace, bypassing the documented isolation boundary. This issue has been patched in versions 2.11.43, 3.6.14, and 3.7.0-rc.2.

Timeline

1. Apr 30, 2026, 8:20 PM UTCCVE published
2. May 4, 2026, 1:25 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

3. May 4, 2026, 1:26 PM UTCRecord last updated

Affected versions

• traefik traefik

  fixed in 2.11.43; From 3.7.0-ea.1 · fixed in 3.7.0-rc.2

• github.com/traefik/traefikGo

  All versions

• github.com/traefik/traefik/v2Go

  fixed in 2.11.43

• github.com/traefik/traefik/v3Go

  From 3.0.0-beta1 · fixed in 3.6.14; From 3.7.0-ea.1 · fixed in 3.7.0-rc.2

• github.com/traefik/traefik/v3Go

  From 3.7.0-ea.1 · fixed in 3.7.0-rc.2

• github.com/traefik/traefik/v3Go

  From 3.0.0-beta1 · fixed in 3.6.14

• github.com/traefik/traefikGo

  through 1.7.34

References 5