Claude Desktop Preauthorizes Browser Extension Access on macOS, Raising Privacy Concerns

Summary

Anthropic's Claude Desktop for macOS installs a Native Messaging manifest file that pre-authorizes the Claude browser extension and two other Chromium extension IDs. The manifest is created for Chromium-based browsers even when those browsers are not installed, meaning any future Chromium browser added to the machine will automatically grant preauthorized extensions access to a local binary running outside the browser sandbox. This enables extensions to read pages, fill forms, capture screens, and access authenticated sessions without additional consent. Security researcher Alexander Hanff discovered the file, and Noah Kenney independently reviewed the findings. The behavior raises privacy and legal questions, including potential breaches of the ePrivacy Directive Article 5(3).