CVE-2026-63128

A flaw was found in rmcp, a Rust SDK for the Model Context Protocol. An unauthenticated remote attacker can send specially crafted JSON-RPC POST requests to the stateful Streamable HTTP server. These requests cause the server to create and permanently retain session and channel state without proper validation. Repeated exploitation of this vulnerability can lead to unbounded growth of the session table, resource exhaustion, and ultimately a Denial of Service (DoS) for the server.

Important: This flaw allows an unauthenticated remote attacker to cause a denial of service by exhausting server memory and resources. The rmcp Rust SDK, when used to implement a stateful Streamable HTTP server, is susceptible to resource exhaustion due to improper session management, which can impact legitimate client latency and terminate the server process.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

To mitigate this issue, restrict network access to the service utilizing the rmcp Streamable HTTP server to trusted clients only. Implement firewall rules to limit inbound connections to the specific port and IP addresses where the vulnerable service is exposed.