CVE-2026-59950: CWE-346: Origin Validation Error in modelcontextprotocol python-sdk
The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to 1.28.1, the deprecated mcp.server.websocket.websocket_server transport accepted WebSocket handshakes without applying Host or Origin header validation, leaving no SDK-level way to restrict which origins could connect to applications that exposed that transport. This issue is fixed in version 1.28.1.
AI Analysis
Technical Summary
CVE-2026-59950 describes a vulnerability in the MCP Python SDK's deprecated mcp.server.websocket.websocket_server transport, where WebSocket handshake requests did not validate the Host or Origin headers. This lack of origin validation means that applications exposing this transport could not restrict which origins were allowed to connect, potentially allowing unauthorized cross-origin WebSocket connections. The vulnerability is resolved in version 1.28.1 of the SDK.
Potential Impact
The vulnerability allows WebSocket connections from any origin due to missing Host and Origin header validation. This can lead to unauthorized cross-origin access to applications using the affected transport, potentially exposing sensitive data or functionality. The CVSS 4.0 score is 7.6 (high severity), indicating significant impact with network attack vector, low attack complexity, and partial user interaction required.
Mitigation Recommendations
Upgrade to version 1.28.1 or later of the MCP Python SDK, where the origin validation issue has been fixed. Since this is a client-side SDK and not a cloud service, users must apply the update themselves to remediate the vulnerability. Patch status is confirmed fixed in 1.28.1.
CVE-2026-59950: CWE-346: Origin Validation Error in modelcontextprotocol python-sdk
Description
The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to 1.28.1, the deprecated mcp.server.websocket.websocket_server transport accepted WebSocket handshakes without applying Host or Origin header validation, leaving no SDK-level way to restrict which origins could connect to applications that exposed that transport. This issue is fixed in version 1.28.1.
CVSS v4.0
Score 7.6high
Affected software
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AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-59950 describes a vulnerability in the MCP Python SDK's deprecated mcp.server.websocket.websocket_server transport, where WebSocket handshake requests did not validate the Host or Origin headers. This lack of origin validation means that applications exposing this transport could not restrict which origins were allowed to connect, potentially allowing unauthorized cross-origin WebSocket connections. The vulnerability is resolved in version 1.28.1 of the SDK.
Potential Impact
The vulnerability allows WebSocket connections from any origin due to missing Host and Origin header validation. This can lead to unauthorized cross-origin access to applications using the affected transport, potentially exposing sensitive data or functionality. The CVSS 4.0 score is 7.6 (high severity), indicating significant impact with network attack vector, low attack complexity, and partial user interaction required.
Mitigation Recommendations
Upgrade to version 1.28.1 or later of the MCP Python SDK, where the origin validation issue has been fixed. Since this is a client-side SDK and not a cloud service, users must apply the update themselves to remediate the vulnerability. Patch status is confirmed fixed in 1.28.1.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-07-07T18:49:15.607Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a57f21668715ace4371edee
Added to database: 07/15/2026, 20:48:22 UTC
Last enriched: 07/22/2026, 22:55:03 UTC
Last updated: 08/28/2026, 22:52:12 UTC
Views: 194
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