The report
A reverse proxy's maximum request size is not a complete limit on the work an MCP server can be asked to perform. The TypeScript MCP SDK advisory describes HTTP handlers that accepted unbounded message bodies or excessively long JSON-RPC batches, creating memory and processing exhaustion risk for network-reachable services. The report does not claim widespread observed outages. Issue description.
The corrected releases introduce two different defaults: a 4 MiB body limit, returning HTTP 413 for oversized content, and a 100-message batch cap, returning HTTP 400 for batches above the threshold. The listed fixes include SDK 1.30.1, server 2.1.0, Node 2.1.0 and Hono 2.0.1 packages. A body-size limit alone cannot bound the number of cheap but cumulatively expensive operations in a small JSON payload. Patch details.
The advisory's remotely reachable attack surface is the affected HTTP transport, not stdio-only MCP installations. Actual exposure therefore depends on routing, authentication, outer request limits and whether batches are accepted at that entry point. A useful regression test checks the two limits independently, including a compact batch of more than 100 requests and a single oversized message. Scope qualification.
This is a capacity boundary, not evidence that a model was tricked into making a harmful decision. It belongs in the same operational review as tool authorization, but cannot be solved by better prompts or content filtering. Primary security advisory.