CVE-2026-32695: Traefik has Knative Ingress Rule Injection that Allows Host Restriction Bypass

There is a potential vulnerability in Traefik’s Kubernetes Knative, Ingress, and Ingress-NGINX providers related to rule injection.

User-controlled values are interpolated into backtick-delimited Traefik router rule expressions without escaping or validation. A malicious value containing a backtick can terminate the literal and inject additional operators into Traefik’s rule language, altering the parsed rule tree. In shared or multi-tenant deployments, this can bypass host and header routing constraints and redirect unauthorized traffic to victim services.

Traefik’s Knative provider builds router rules by interpolating user-controlled values into backtick-delimited rule expressions without escaping. In live cluster validation, Knative rules[].hosts[] was exploitable for host restriction bypass (for example tenant.example.com) || Host(attacker.com), producing a router that serves attacker-controlled hosts. Knative headers[].exact also allows rule-syntax injection and proves unsafe rule construction. In multi-tenant clusters, this can route unauthorized traffic to victim services and lead to cross-tenant traffic exposure. Severity is High in shared deployments.

Tested on Traefik v3.6.10; the vulnerable pattern appears to have been present since the Knative provider was introduced. Earlier versions with Knative provider support are expected to be affected.