GHSA-46wh-3698-f2cx: Traefik: Deny Rule Bypass via Unauthenticated Malicious gRPC Requests in gRPC-Go Dependency (CVE-2026-33186)

There is a potential vulnerability in Traefik due to its dependency on an affected version of gRPC-Go (CVE-2026-33186).

A remote, unauthenticated attacker can send gRPC requests with a malformed HTTP/2 :path pseudo-header omitting the mandatory leading slash (e.g., Service/Method instead of /Service/Method). While the server routes such requests correctly, path-based authorization interceptors evaluate the raw non-canonical path and fail to match “deny” rules, allowing the request to bypass the policy entirely if a fallback “allow” rule is present.

This CVE hits traefik until Version 3.6.11 and 2.11.41. gRPC-Go has an authorization bypass via missing leading slash in :path