What’s Vulnerable › Vulnerabilities

CVE-2026-59950: MCP Python SDK: WebSocket server transport does not support Host/Origin validation

• Severity: high (CVSS 8.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-15 · updated 2026-10-24
• Weakness: CWE-346

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.

Affected products

• modelcontextprotocol python-sdk: before 1.28.1 — fixed in 1.28.1

How to fix

Upgrade to a fixed version: modelcontextprotocol python-sdk 1.28.1. Check the vendor advisory for mitigations.

References

• https://github.com/modelcontextprotocol/python-sdk/commit/777b8d06710c140e3606b0d4598e2aa48546c266
• https://github.com/modelcontextprotocol/python-sdk/pull/2992
• https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.28.1
• https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-vj7q-gjh5-988w

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