CVE-2026-85594 is an access control flaw in the Traefik Kubernetes Ingress provider, versions v3.7.1 to v3.7.10 (NVD 9.8, Traefik rates it medium). A tenant could attach an operator owned middleware to its Service. Upgrade to v3.7.11. The sections below cover affected versions, how to check your exposure and what to do first.
What's affected
The advisory lists Traefik v3.7.1 through v3.7.10, patched in v3.7.11. The weakness is CWE-639, authorization bypass through a user controlled key. The crossProviderNamespaces allowlist was enforced for the router.middlewares and service.serverstransport annotations, but not for the traefik.ingress.kubernetes.io/service.middlewares Service annotation.
A tenant in a namespace outside the allowlist could attach an operator owned middleware to its own Service and, if that middleware injects a backend credential, recover it at a backend the tenant controls. The option was introduced in v3.7.1, so Traefik v2 and v3 up to v3.6 are not affected. Traefik rates the issue medium, while NVD shows 9.8. The record is not in the CISA KEV catalog.
How to check if you're exposed
Check the Traefik version.
kubectl get pods -A -o jsonpath='{..image}' | tr " " "\n" | grep traefik | sort -u
Then check whether you enable crossProviderNamespaces on the Kubernetes Ingress provider and whether you allow tenants to create Services in their own namespaces. If you do not use the option, the advisory's scenario does not apply.
What to do now
- Upgrade Traefik to v3.7.11 or later.
- Review middlewares that inject backend credentials and who can reference them.
- Check which namespaces are on the crossProviderNamespaces allowlist.
- Restrict who can annotate Services in shared clusters.
- Rotate any backend credential injected through a middleware that tenants could reach.
Why it matters
The allowlist was a good control that did not cover every annotation. Each place where tenants can reference something owned by someone else needs the same check, and a missing one becomes a bypass.
In multi tenant clusters, review which annotations your ingress controller reads from tenant owned objects. That list is the real trust boundary.
Try it yourself
Click through it at your own pace, or open it full screen.
Quick check
Why do the scores differ?
NVD scored it 9.8 from the record text, and the Traefik advisory calls it medium because it needs a tenant with namespace access and a credential injecting middleware.
Sources
Last reviewed: 19 October 2026.
