CVE-2026-59950
HighCVSS 8.1Exploitation Probability (EPSS)
Low risk5th percentile - higher than 5% of all known CVEs
Summary
A vulnerability in the MCP Python SDK (mcp) prior to version 1.28.1 affects the deprecated WebSocket transport, which did not validate Host or Origin headers. This allowed arbitrary third parties to establish WebSocket connections to applications using that transport.
Risk Assessment
The organization is at risk of unauthorized access to applications using the deprecated WebSocket transport, potentially leading to data leakage or session hijacking by an attacker.
Recommendation
Immediately update the mcp library to version 1.28.1 or later. If not possible, disable the deprecated WebSocket transport and replace it with a more secure alternative.
Other vulnerabilities in MCP Python SDK
See all- CVE-2026-52870High
A vulnerability in the MCP Python SDK (mcp) versions 1.23.0 through 1.27.2 allows any client to access other clients' tasks. Default handlers for task operations do not verify the session, enabling enumeration, reading results, consuming messages, or canceling tasks of other clients.
- CVE-2026-52869High
A vulnerability in MCP Python SDK (mcp) before version 1.27.2 allows an attacker to inject JSON-RPC messages into an existing session. The issue affects SSE and Streamable HTTP transports, which do not verify the authenticated client's identity when using the session_id parameter or Mcp-Session-Id header.
Original NVD description (English source)
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.