"Claudy Day" Three-Stage Attack Chain Exfiltrates Data via Anthropic's Own Files API

Security researchers disclosed a chained exploit combining invisible prompt injection via URL parameters, silent data exfiltration through an attacker's Anthropic Files API account (bypassing network monitoring), and an open redirect on claude.com abused via Google Ads. Anthropic patched the injection vector; exfil and redirect mitigations remain in progress. The use of Anthropic's own infrastructure as the exfil channel is the operationally novel detail. Source