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

• Go github.com/traefik/traefik/v2: < 2.11.42 → fixed in 2.11.42 • Go github.com/traefik/traefik/v3: >= 3.0.0-beta3, < 3.6.12 → fixed in 3.6.12 • Go github.com/traefik/traefik/v3: >= 3.7.0-ea.1, < 3.7.0-ea.3 → fixed in 3.7.0-ea.3

Summary 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. Patches • https://github.com/traefik/traefik/releases/tag/v2.11.42 • https://github.com/traefik/traefik/releases/tag/v3.6.12 • https://github.com/traefik/traefik/releases/tag/v3.7.0-ea.3 For more information If there are any questions or comments about this advisory, please open an issue. Original Description Summary 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 Details As described in https://github.com/advisories/GHSA-p77j-4mvh-x3m3 PoC Update library version in https://github.com/traefik/traefik/blob/67c64ed9b25fbb90f1086977a62827133a7aa01b/go.mod#L108 Impact Is described in https://github.com/advisories/GHSA-p77j-4mvh-x3m3 ----------