Vulnerability Details CVE-2026-52869
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.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.003
EPSS Ranking 16.3%
CVSS Severity
CVSS v3 Score 7.1
References
- https://github.com/modelcontextprotocol/python-sdk/commit/1abcca2408a6b50e10ec601181f63f9978705c00
- https://github.com/modelcontextprotocol/python-sdk/commit/ce267b6fc515dc4efc1dc70b6975b16ff0feef0a
- https://github.com/modelcontextprotocol/python-sdk/pull/2690
- https://github.com/modelcontextprotocol/python-sdk/pull/2719
- https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2
- https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-jpw9-pfvf-9f58
Products affected by CVE-2026-52869
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cpe:2.3:a:lfprojects:mcp_python_sdk:0.2.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:0.3.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:0.5.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:0.6.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:0.8.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:0.9.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:0.9.1
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.0.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.1.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.1.1
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.1.2
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.1.3
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.10.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.10.1
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.11.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.12.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.12.1
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.12.2
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.12.3
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.12.4
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.13.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.13.1
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.14.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.14.1
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.15.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.16.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.17.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.18.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.19.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.2.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.2.1
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.20.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.21.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.21.1
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.21.2
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.22.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.23.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.23.1
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.23.2
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.23.3
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.24.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.25.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.26.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.27.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.27.1
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.3.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.4.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.4.1
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.5.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.6.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.7.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.7.1
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.8.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.8.1
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.9.0
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.9.1
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.9.2
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.9.3
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cpe:2.3:a:lfprojects:mcp_python_sdk:1.9.4