CVE-2026-52869
Last modified
CVE-2026-52869 is a high-severity vulnerability rated 7.1/10 on the CVSS scale. 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. EPSS estimates a 0.25% chance of exploitation in the next 30 days.
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.
Metrics
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L
Weakness Enumeration
Affected Software
| Vendor | Product | Versions |
|---|---|---|
| Lfprojects | Mcp Python Sdk | < 1.27.2 |
References
- https://github.com/modelcontextprotocol/python-sdk/pull/2690Issue Tracking, Patch
- https://github.com/modelcontextprotocol/python-sdk/pull/2719Issue Tracking, Patch
Timeline
- Published
- Last Modified
- Status
- Analyzed
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