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Traefik is an HTTP reverse proxy and load balancer. Prior to 3.6.21 and 3.7.5, there is a high severity vulnerability in Traefik's Kubernetes Gateway provider affecting the crossProviderNamespaces allowlist. For HTTPRoute rules that declare multiple (WRR) backendRefs, Traefik evaluates the allowlist against the target backendRef.namespace instead of the route's own namespace. As a result, an HTTPRoute created in a namespace that is not allow-listed can reference a cross-provider TraefikService such as api@internal, dashboard@internal or rest@internal by pointing backendRef.namespace at an allow-listed namespace covered by a Gateway API ReferenceGrant, exposing internal Traefik services on the data plane. Exploitation requires the ability to create an accepted HTTPRoute and a matching ReferenceGrant from an allow-listed namespace; it does not require any change to Traefik static configuration, RBAC, or the deployment itself. This vulnerability is fixed in 3.6.21 and 3.7.5.

GHSA-3g6v-2r68-prfc — Traefik: Kubernetes Gateway crossProviderNamespaces bypass allows HTTPRoute outside the allowlist to expose internal Tr…

Affected: Go: github.com/traefik/traefik/v3, Go: github.com/traefik/traefik/v2, Go: github.com/traefik/traefik

## Summary

There is a high severity vulnerability in Traefik's Kubernetes Gateway provider affecting the `crossProviderNamespaces` allowlist. For `HTTPRoute` rules that declare multiple (WRR) backendRefs, Traefik evaluates the allowlist against the target `backendRef.namespace` instead of the route's own namespace. As a result, an `HTTPRoute` created in a namespace that is not allow-listed can reference a cross-provider `TraefikService` such as `api@internal`, `dashboard@internal` or `rest@internal` by pointing `backendRef.namespace` at an allow-listed namespace covered by a Gateway API `ReferenceGrant`, exposing internal Traefik services on the data plane. Exploitation requires the ability to create an accepted `HTTPRoute` and a matching `ReferenceGrant` from an allow-listed namespace ; it does not require any change to Traefik static configuration, RBAC, or the deployment itself.

## Patches

- https://github.com/traefik/traefik/releases/tag/v3.6.21 - https://github.com/traefik/traefik/releases/tag/v3.7.5

## For more information

If you have any questions or comments about this advisory, please [open an issue](https://github.com/traefik/traefik/issues).

<details> <summary>Original Description</summary>

# Summary

The Kubernetes Gateway provider's `crossProviderNamespaces` option is documented as restricting which Gateway API route namespaces may declare `TraefikService` backendRefs.

For `HTTPRoute` rules with multiple backendRefs, Traefik checks this allowlist against…

openSUSE-SU-2026:11251-1 — traefik-3.7.7-1.1 on GA media

traefik-3.7.7-1.1 on GA media