The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP). From 1.8.0 until 1.30.0 and 2.2.0, stateful Streamable HTTP servers, including FastMCP, MCPServer, Server.streamable_http_app(), and StreamableHTTPSessionManager, retain session entries without an idle expiration or aggregate session-count limit. DELETE, refused opening requests, and completed sessions do not reliably discard their entries, and each entry can retain parsed initialize parameters. A client that can reach the endpoint can therefore create ordinary short requests that grow server memory without bound until restart. Stateless HTTP, stdio, and SSE transports are not affected. This issue is fixed in versions 1.30.0 and 2.2.0.
Fix
Nothing published yet: no patch, vendor advisory or mitigation reference on NVD, no vendor advisory in the News for this CVE, not in CISA's KEV, no fixed package version. BaselineWatch does not guess at one.
Change history 2
- StatusReceived → Awaiting AnalysisNVD modified 2026-10-16 16:00
- First seenCVSS 6.9NVD modified 2026-10-14 17:18
Affected (CPE criteria) 0
NVD has not attached CPE configurations yet.
References 7
- https://github.com/modelcontextprotocol/python-sdk/commit/92120b4b0f50385af096592d7cee932fc1d994e7
- https://github.com/modelcontextprotocol/python-sdk/commit/d2290ca3434731b68ea3e2270bc06a6e6575931b
- https://github.com/modelcontextprotocol/python-sdk/pull/3395
- https://github.com/modelcontextprotocol/python-sdk/pull/3426
- https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.30.0
- https://github.com/modelcontextprotocol/python-sdk/releases/tag/v2.2.0
- https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-84m7-p3x7-pcfv