CVE-2026-100347: kin-openapi: Unauthenticated panic (DoS) in openapi3filter legacy router via non-canonical/unsupported HTTP method on a static path

The openapi3filter.ValidationHandler (the exported, documented request-validation middleware) hard-wires the legacy router (routers/legacy). That router matches the incoming request method verbatim against a trie built exclusively from upper-cased canonical HTTP methods. A request carrying a method token that is not one of the 9 standard methods — a legitimate-but-unsupported token such as PROPFIND, or a non-canonical case variant such as lowercase get — misses the trie, leaves route == nil, and for an existing static path falls through to PathItem.GetOperation(method), whose default: case calls panic(...). The panic fires inside route resolution, before any authentication runs. This is an unauthenticated, remotely triggerable denial of service (recovered per-connection panic + unbounded error-log growth).