Rmcp versions prior to 3.9.0 contain a vulnerability in their built-in Streamable HTTP clients where response bodies are buffered in memory without size limits. This affects the reqwest and Unix socket clients, causing them to fully buffer certain HTTP responses, including application/json POST responses and non-2xx error responses. A malicious or compromised MCP server can exploit this by sending an unending response body, leading to memory exhaustion and process termination. The issue is fixed in version 3.9.0 by imposing strict size limits on response bodies and rejecting oversized content.