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CVE-2026-52869

7.1 high SSVC exploitation: none Analyzed
NVD · CVE.org

The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to 1.27.2, the SSE and stateful Streamable HTTP transports mcp.server.sse.SseServerTransport and mcp.server.streamable_http_manager.StreamableHTTPSessionManager route requests to existing sessions using only the session_id query parameter or Mcp-Session-Id header without verifying the authenticated principal that created the session, allowing a different bearer-token-authenticated client with a known session ID to inject JSON-RPC messages into that session. This issue is fixed in version 1.27.2.

Fix

Patch, vendor advisory and mitigation references on NVD 5

Every line above is quoted from NVD, CISA, Microsoft, the vendor's own advisory or DISA; nothing is generated.

Change history 1

  1. First seenCVSS 7.1 · lfprojectsNVD modified 2026-10-24 21:10

Affected (CPE criteria) 1

  • cpe:2.3:a:lfprojects:mcp_python_sdk:*:*:*:*:*:*:*:*

References 6