Flaw in Anthropic Claude Extensions Can Lead to RCE in Google Calendar: LayerX

LayerX researchers disclosed a proof-of-concept vulnerability in Anthropic’s Claude Desktop Extensions (MCP) that allows a calendar event combined with a generic prompt (e.g., “take care of it”) to be autonomously chained to a privileged local MCP server and achieve zero-click remote code execution. Because Claude Desktop Extensions run unsandboxed with full system privileges, this flow can lead to full system compromise; the issue reportedly affects over 10,000 active users and ~50 extensions, and Anthropic declined to fix the behavior, noting the tools require user installation and permission configuration.