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.
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Affected Vendors & Products
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History
Thu, 16 Jul 2026 13:30:00 +0000
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ssvc
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Thu, 16 Jul 2026 00:00:00 +0000
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Modelcontextprotocol
Modelcontextprotocol python-sdk |
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Wed, 15 Jul 2026 20:15:00 +0000
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| Description | 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. | |
| Title | MCP Python SDK: HTTP transports serve session requests without verifying the authenticated principal | |
| Weaknesses | CWE-639 | |
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cvssV3_1
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Status: PUBLISHED
Assigner: GitHub_M
Published:
Updated: 2026-07-16T13:00:37.854Z
Reserved: 2026-06-08T21:44:27.363Z
Link: CVE-2026-52869
Updated: 2026-07-16T13:00:32.557Z
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OpenCVE Enrichment
Updated: 2026-07-15T23:45:15Z