Missing Origin Validation in WebSockets Affecting mcp package, versions [,1.28.1)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-PYTHON-MCP-18016320
- published19 Jul 2026
- disclosed16 Jul 2026
- creditNitish Yaddala,Nadav,KairoKid,Aleksandr Kovalko,u-ktdi
Introduced: 16 Jul 2026
NewCVE-2026-59950 (opens in a new tab)How to fix?
Upgrade mcp to version 1.28.1 or higher.
Overview
mcp is a Model Context Protocol SDK
Affected versions of this package are vulnerable to Missing Origin Validation in WebSockets in the deprecated websocket_server() transport function, which builds a Starlette WebSocket and calls accept(subprotocol='mcp') without inspecting the connection's Host or Origin headers. An attacker can open a WebSocket to a reachable MCP server from a page of any origin and issue JSON-RPC requests on the resulting session, enumerating and invoking tools and accessing resources, by luring a victim to an attacker-controlled webpage while the server runs.