Description
The Model Context Protocol Python SDK is the official Python SDK for Model Context Protocol servers and clients. In mcp versions before 1.29.1 and from 2.0.0a1 through 2.0.1, the Streamable HTTP session manager, SSE message endpoint, and OAuth authorization-server routes buffer complete HTTP request bodies without enforcing a maximum size. An unauthenticated remote client able to reach an affected endpoint can send a large declared or streamed request body that consumes multiple times the body size in process memory and can repeatedly exhaust memory or terminate the server. Stdio-only servers and deployments with an effective upstream request-size limit are not affected, and applications that use StreamableHTTPServerTransport directly remain responsible for enforcing their own limit. The standard SDK server applications and session managers are fixed in versions 1.29.1 and 2.1.0.
References7
- github.com/modelcontextprotocol/python-sdk/commit/03aaebd3aadb2…
- github.com/modelcontextprotocol/python-sdk/commit/4dc224fab201b…
- github.com/modelcontextprotocol/python-sdk/commit/57394b0548d1e…
- github.com/modelcontextprotocol/python-sdk/commit/5f0b6af9f2b0a…
- github.com/modelcontextprotocol/python-sdk/releases/tag/v1.29.1
- github.com/modelcontextprotocol/python-sdk/releases/tag/v2.1.0
- github.com/modelcontextprotocol/python-sdk/security/advisories/…
Metrics
- CVSS 3.1
-
7.5
HIGH
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - EPSS — exploit probability
- 1% percentile: 54 · as of 11 November 2026
- CWE
- CWE-770
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.