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.

CVSS v3 7.1 HIGH

7.1^/10

CVSS v3 : HIGH

Vector :

Exploitability : 1.6 / Impact : 5.5

Attack Vector NETWORK

Attack Complexity HIGH

Privileges Required LOW

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact HIGH

Availability Impact LOW

Scope UNCHANGED

References

Link	Resource
https://github.com/modelcontextprotocol/python-sdk/commit/1abcca2408a6b50e10ec601181f63f9978705c00	Patch
https://github.com/modelcontextprotocol/python-sdk/commit/ce267b6fc515dc4efc1dc70b6975b16ff0feef0a	Patch
https://github.com/modelcontextprotocol/python-sdk/pull/2690	Issue Tracking Patch
https://github.com/modelcontextprotocol/python-sdk/pull/2719	Issue Tracking Patch
https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2	Release Notes
https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-jpw9-pfvf-9f58	Vendor Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:lfprojects:mcp_python_sdk:*:*:*:*:*:*:*:*

History

No history.

Information

Published : 2026-07-15 20:17

Updated : 2026-07-17 18:06

NVD link : CVE-2026-52869

Mitre link : CVE-2026-52869

CVE.ORG link : CVE-2026-52869

JSON object : View

Products Affected

lfprojects

mcp_python_sdk

CWE

CWE-639

Authorization Bypass Through User-Controlled Key

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