CVEs / CVE-2026-59951
CVE-2026-59951
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 · 1
| Product | Versions affected | Fixed in |
|---|---|---|
| Anthropic / MCP project: Model Context Protocol SDKs and reference servers | not stated by CPE | — |
Versions as NVD's CPE configuration states them; "—" means the record gives no fixed version, not that none exists. Check the vendor's advisory in the references.
In this registry
- python-sdk — agent dossier
- typescript-sdk — agent dossier
References · 7
- github.com/modelcontextprotocol/python-sdk/commit/92120b4b0f50385af096592d7cee932fc1d994e7
- github.com/modelcontextprotocol/python-sdk/commit/d2290ca3434731b68ea3e2270bc06a6e6575931b
- github.com/modelcontextprotocol/python-sdk/pull/3395
- github.com/modelcontextprotocol/python-sdk/pull/3426
- github.com/modelcontextprotocol/python-sdk/releases/tag/v1.30.0
- github.com/modelcontextprotocol/python-sdk/releases/tag/v2.2.0
- github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-84m7-p3x7-pcfv
The official record's references, as NVD lists them, minus any tagged Exploit. Nothing here is an exploit or a proof of concept.
Description, scores, versions and references are the official CVE record's own, retrieved 2026-10-25 from NVD. Category, attack surface and cross-links are this registry's classification and can be wrong — use the button above. Not a severity assessment for your deployment.