Model Context Protocol Python SDK Unbounded Session Accumulation Flaw

# Model Context Protocol Python SDK Unbounded Session Accumulation Flaw

https://gcdradar.vercel.app/incidents/model-context-protocol-python-sdk-unbounded-session-accumula · AIR-2026-0324 · closed 2026-10-14

- Lane: Patch now
- Severity: 2 (Disclosed vulnerability)
- Fix status: Fix status unknown
- First reported: 2026-10-14
- AI role: Attack on AI
- Products: mcp
- CVE ids: CVE-2026-59951
- CVSS: 7.5

## Summary

Stateful Streamable HTTP servers in the MCP Python SDK retain session entries indefinitely without expiration limits, allowing resource exhaustion attacks. A security advisory and updates have been provided.

## What to do

No action recorded; read the sources below and the vendor's advisory.

## Latest updates

- 2026-10-15: CVE-2026-59951: MCP Python SDK: Unbounded Session Accumulation in StreamableHTTP Transport Enables Resource Exhaustion (https://github.com/advisories/GHSA-84m7-p3x7-pcfv)
- 2026-10-14: CVE-2026-59951: The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP). (https://nvd.nist.gov/vuln/detail/CVE-2026-59951)

## Sources

- 2026-10-14 NVD: CVE-2026-59951: The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP). https://nvd.nist.gov/vuln/detail/CVE-2026-59951
- 2026-10-15 GitHub Advisory Database: CVE-2026-59951: MCP Python SDK: Unbounded Session Accumulation in StreamableHTTP Transport Enables Resource Exhaustion https://github.com/advisories/GHSA-84m7-p3x7-pcfv

Verify against the vendor's advisory before changing production. Data CC BY-SA 4.0, https://gcdradar.vercel.app.