MCPA-2026-0034
highauth-missing
MCP Python SDK WebSocket server transport lacks Host/Origin validation (CVE-2026-59950)
The MCP Python SDK (PyPI: mcp) before 1.28.1: the deprecated WebSocket server transport (mcp.server.websocket.websocket_server) accepted the WebSocket handshake without any Host or Origin header validation — the TransportSecuritySettings mechanism used by the SSE and Streamable HTTP transports was not wired into it, enabling DNS-rebinding / cross-origin access to locally hosted servers. Fixed in 1.28.1.
Affected packages
| Ecosystem | Package | Affected versions |
|---|---|---|
| pypi | mcp | >= 0, < 1.28.1 |
Identifiers
CVE-2026-59950GHSA-vj7q-gjh5-988wCWE-346CWE-1385
References
- advisory https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-vj7q-gjh5-988w
- web https://nvd.nist.gov/vuln/detail/CVE-2026-59950
- fix https://github.com/modelcontextprotocol/python-sdk/pull/2992
- web https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.28.1
Timeline
- Published: 2026-07-16