AIKIDO-2026-329399

TL;DR

In its default configuration MCP::Server::Transports::StreamableHTTPTransport never expires sessions, storing a new ServerSession for every successful initialize request and only removing it on an explicit client DELETE. An unauthenticated attacker can repeatedly initialize sessions and disconnect, forcing the server to retain an unbounded number of session objects until memory is exhausted. This causes a memory-exhaustion denial of service via an initialize flood. The fix bounds retention with a finite default session_idle_timeout and a max_sessions cap that rejects new sessions with HTTP 503.