Claude Desktop Extensions CVSS 10 Zero-Click RCE — Anthropic Declined to Fix.

LayerX Security disclosed a CVSS 10/10 zero-click RCE affecting 10,000+ DXT users — a single malicious Google Calendar event achieves full system compromise because DXT MCP servers run with full host privileges and no sandboxing. Critically, Anthropic stated it "falls outside our current threat model." This creates a new risk category: when upstream vendors explicitly decline to patch critical vulnerabilities, builders must implement their own trust boundaries. What to do: Audit which DXT extensions have executor access. Treat any MCP connector processing external data as a potential injection vector.