Vulnerability in modelcontextprotocol rust-sdk

[ Why it matters ]Priority signals

• Public proof-of-concept exploit exists (CISA SSVC)

[ Description ]Official description

RMCP is an official Rust SDK for the Model Context Protocol. Prior to 2.0.0, the rmcp crate's stateful Streamable HTTP server in crates/rmcp/src/transport/streamable_http_server/tower.rs allows an unauthenticated client to send a well-formed JSON-RPC POST that is not an initialization request, or an initialization request with a mismatched protocol header, causing StreamableHttpService::handle_post to call LocalSessionManager.create_session before validating the message. An early validation failure returns without removing the inserted LocalSessionHandle from LocalSessionManager.sessions, permanently retaining session and channel state for the server process lifetime. Repeated requests can grow the shared session table without bound, degrade legitimate-client latency through lock contention, exhaust memory, and terminate the server. This issue is fixed in version 2.0.0.

[ Fixes ]Fixes and patches

No fix or interim patch is linked from our sources yet. Check the vendor references below and limit exposure of affected systems until a fix is available.

[ Advisories ]Government CERT advisories

• BSI CERT-Bund12 Oct 2026WID-SEC-2026-3883

  Red Hat Enterprise Linux (goose, environment-modules, tornado): Multiple vulnerabilities Translated from German

  Risk highCVE-2026-93599CVE-2026-63128CVE-2026-103262+3 more CVEs

[ References ]References

• github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-9pj6-vhgr-3mwhx_refsource_CONFIRM
• github.com/modelcontextprotocol/rust-sdk/pull/934x_refsource_MISC
• github.com/modelcontextprotocol/rust-sdk/commit/dfa7fd6f9309deab60bea230b041be9a3fcda846x_refsource_MISC
• github.com/modelcontextprotocol/rust-sdk/releases/tag/rmcp-v2.0.0x_refsource_MISC