MCP TypeScript SDK Security Advisory: HTTP Server Transport Layer and Handlers Do Not Limit Request Body Size or JSON-RPC Batch Length
MCP TypeScript SDK: HTTP server transports and handlers did not limit request body size or JSON-RPC batch length
The MCP TypeScript SDK released a security advisory: its HTTP server transport layer and handlers do not limit the size of POST request bodies or the number of JSON-RPC batch messages, so large requests can exhaust server memory and a single long batch can block the service, and this can be exploited without credentials. Only servers reachable via Streamable HTTP are affected; servers using only stdio are not affected, and parsers such as express.json() cannot provide protection because they do not limit batch length. Affected versions are @modelcontextprotocol/sdk 1.10.0 and above, before 1.30.1; @modelcontextprotocol/server and @modelcontextprotocol/node 2.0.0 and above, before 2.1.0; and @modelcontextprotocol/hono 2.0.0 and above, before 2.0.1; these have been fixed in 1.30.1, 2.1.0 and 2.0.1 respectively.
The advisory lists the affected and fixed versions for each package and provides a temporary reverse proxy mitigation; teams deploying MCP HTTP services can use it to investigate and upgrade.