mcp-framework Denial-of-Service Vulnerability via Unbounded HTTP Request Body Handling

A denial-of-service vulnerability has been identified in mcp-framework versions through 0.2.21. The issue arises in the readRequestBody() function of the HTTP transport, where request body chunks are concatenated into a string without any size limit. Although a maxMessageSize configuration option exists, it is not enforced, allowing remote unauthenticated attackers to send large POST requests to /mcp, causing memory exhaustion and crashing the server.

Impact

Exploitation of this vulnerability leads to memory exhaustion, causing the server to crash. The readRequestBody() function processes data before any authentication checks, and the existing maxMessageSize configuration is not enforced, creating a false sense of security.

Reproduction

The vulnerability can be reproduced by sending a large POST request, such as one exceeding 50MB, to the /mcp endpoint of an mcp-framework HTTP server. This can be done using tools like Postman or curl, by selecting the 'POST' method and uploading a large file as the request body.

Remediation

Users can update to mcp-framework version 0.2.22 or later, where this vulnerability has been fixed.