CVE-2026-63128: modelcontextprotocol rust-sdk Uncontrolled Resource Consumption

Vulnerability summary

CVE-2026-63128 is a high (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in modelcontextprotocol rust-sdk. EPSS estimates a 0.63% chance of exploitation in the next 30 days, higher than 49.2% of scored vulnerabilities.

Timeline

1. 16-09-2026
   PublishedVulnerability first disclosed.
2. 16-09-2026
   Last modifiedVulnerability information updated.

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.

• CWE-400Uncontrolled Resource ConsumptionThe product does not properly control the allocation and maintenance of a limited resource.
• CWE-401Missing Release of Memory after Effective LifetimeThe product does not sufficiently track and release allocated memory after it has been used, making the memory unavailable for reallocation and reuse.
• CWE-772Missing Release of Resource after Effective LifetimeThe product does not release a resource after its effective lifetime has ended, i.e., after the resource is no longer needed.