CVE-2026-52869 (GCVE-0-2026-52869)

Vulnerability from cvelistv5 – Published: 2026-07-15 20:06 – Updated: 2026-07-16 13:00
VLAI
Title
MCP Python SDK: HTTP transports serve session requests without verifying the authenticated principal
Summary
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.
Severity
7.1 (High)
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L
SSVC
Exploitation: none Automatable: no Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-07-16 13:00 UTC
CWE
  • CWE-639 - Authorization Bypass Through User-Controlled Key
Assigner
GitHub_M CNA under the mitre root
CNA scorecard C 72/100 over 8035 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
modelcontextprotocol python-sdk Affected: < 1.27.2
guessed Create a notification for this product.
Show details on NVD website
To clipboard 

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