6.9
Medium
CVE-2026-59951 The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP)
Description
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.
Affected products and versions
| Product | Affected versions | Fixed in |
|---|---|---|
| python-sdk 2.0 | 2.0.0 → < 2.2.0 | 2.2.0 |
| python-sdk 1.8 | 1.8.0 → < 1.30.0 | 1.30.0 |
References
- github.com github.com
- github.com github.com
- github.com github.com
- github.com github.com
- github.com github.com
- github.com github.com
- github.com github.com
Timeline
- Published
- Last modified
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