AIKIDO-2026-248348

TL;DR

The HTTP client transport in MCP::Client::HTTP reads server responses through an incremental streaming callback that buffers Server-Sent Events and JSON response bodies in memory. A message the server never completes, such as an SSE event or JSON body without a terminator, is appended to the in-memory buffer with no size limit. A malicious or compromised MCP server can exploit this to grow the client's memory until the process is exhausted, causing a denial of service. The fix enforces a configurable maximum per-message size on both the SSE and JSON paths and aborts the stream when the limit is exceeded.