CVE-2026-59951
Reported by github_m · Published October 14, 2026
mcp is fixed in 2.2.0 and 1.30.0 (PyPI)
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.
Fixed versions
Upgrade to a fixed version or later. Language registries are listed first, then Linux distributions, then vendor products.
| Package | Ecosystem | Fixed in |
|---|---|---|
| mcp | PyPI | 2.2.0, 1.30.0 |
Risk scores
Affected products
| Vendor | Product | Versions |
|---|---|---|
| modelcontextprotocol | python-sdk | >= 1.8.0, < 1.30.0, >= 2.0.0, < 2.2.0 |
| PyPI | mcp | 1.8.0, 2.0.0 |
| modelcontextprotocol | python-sdk | 2.0.0, 1.8.0 |
| wolfi | semgrep | 0 |
| chainguard | open-webui | 0 |
| chainguard | nemo-gym | 0 |
| wolfi | open-webui | 0 |
| chainguard | semgrep | 0 |
| modelcontextprotocol | python-sdk | |
| chainguard | nemo-rl-cuda-13.0 | 0 |
Timeline
- Oct 14, 2026 Coalition ESS Score
- Oct 14, 2026 CVE Published
- Oct 15, 2026 EPSS Score (6 in total, the first dated here)
- Oct 15, 2026 CVE Updated
- Oct 30, 2026 Security Advisory
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References
- https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-84m7-p3x7-pcfv x_refsource_CONFIRM
- https://github.com/modelcontextprotocol/python-sdk/pull/3395 x_refsource_MISC
- https://github.com/modelcontextprotocol/python-sdk/pull/3426 x_refsource_MISC
- https://github.com/modelcontextprotocol/python-sdk/commit/92120b4b0f50385af096592d7cee932fc1d994e7 x_refsource_MISC
- https://github.com/modelcontextprotocol/python-sdk/commit/d2290ca3434731b68ea3e2270bc06a6e6575931b x_refsource_MISC
- https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.30.0 x_refsource_MISC
- https://github.com/modelcontextprotocol/python-sdk/releases/tag/v2.2.0 x_refsource_MISC
- https://nvd.nist.gov/vuln/detail/CVE-2026-59951 advisory
- https://github.com/advisories/GHSA-84m7-p3x7-pcfv advisory