Claude Desktop extensions allow zero-click RCE via Google Calendar

Feb 2026

LayerX Labs discovered a zero-click remote code execution vulnerability in Claude Desktop Extensions, rated CVSS 10/10. A malicious prompt embedded in a Google Calendar event could trigger arbitrary code execution on the host machine when Claude processes the event data. The attack exploited the gap between a "low-risk" connector and a local MCP server with full code-execution capabilities and no sandboxing. Anthropic declined to fix it, stating it "falls outside our current threat model."