7.1
High
CVE-2026-52869 The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP)
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.
Affected products and versions
| Product | Affected versions | Fixed in |
|---|---|---|
| python-sdk 1.27 | earliest → < 1.27.2 | 1.27.2 |
References
- github.com github.com
- github.com github.com
- github.com github.com
- github.com github.com
- github.com github.com
- github.com github.com
Timeline
- Published
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