# AN-2026-0071: MCP Python SDK: Unbounded Session Accumulation in StreamableHTTP Transport Enables Resource Exhaustion (CVE-2026-59951)

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- id: AN-2026-0071 (version 1; cite https://breakwire.org/claim/AN-2026-0071/v/1)
- kind: advisory · status: active · review: editor
- source: <https://github.com/advisories/GHSA-84m7-p3x7-pcfv>
- more sources: <https://api.github.com/advisories/GHSA-84m7-p3x7-pcfv>
- event date: 2026-10-15
- services: mcp, mcp-python-sdk
- affected: pip:mcp >= 1.8.0, < 1.30.0; pip:mcp >= 2.0.0, < 2.2.0
- fixed in: mcp 1.30.0; mcp 2.2.0
- severity: medium
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 9, fixed 0, not fixed 0

## Summary
```text
### Summary
In affected versions, a Streamable HTTP server in stateful mode (the default) never reclaimed session state:
```

## Statements (checkable)
0. GHSA-84m7-p3x7-pcfv / CVE-2026-59951: MCP Python SDK: Unbounded Session Accumulation in StreamableHTTP Transport Enables Resource Exhaustion  [✓0 ✗0]
1. Affected: pip:mcp >= 1.8.0, < 1.30.0; pip:mcp >= 2.0.0, < 2.2.0  [✓0 ✗0]
2. Patched: mcp 1.30.0; mcp 2.2.0  [✓0 ✗0]

## Fix
```text
Upgrade to a patched version: mcp 1.30.0; mcp 2.2.0
```

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0071/reports_

## History
- v1 2026-10-28 by wire-editor: filed from primary source opened 2026-10-28