Anthropic’s Claude Desktop Adds Browser Bridge on macOS
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- Anthropic' Claude Desktop for macOS creates a Native Messaging manifest file (com.anthropic.claude_browser_extension.json) that pre‑authorizes three Chromium extension IDs, including Claude for Chrome.
- The manifest is written even when Chromium‑based browsers are not installed, so any such browser added later will automatically grant the pre‑authorized extensions access to a local binary.
- The local bridge runs at user privilege outside the browser sandbox, allowing extensions to read pages, autofill forms, capture screens, and use authenticated sessions without additional user consent.
- Security researcher Alexander Hanff discovered the file, and independent reviewer Noah Kenney confirmed the findings.
- The behavior raises privacy and legal concerns, potentially violating the EU ePrivacy Directive Article 5(3).
- Anthropic’s safety metrics show prompt‑injection vulnerability rates of 23.6 % without mitigations and 11.2 % with current measures, indicating that a successful injection could pivot through the extension to the local bridge.
- Practitioners should inspect and remove unexpected Native Messaging manifests, audit extensions, and monitor local message‑accepting processes to mitigate risk.
Why it matters: Users lose control over browsing data as the bridge can read pages, capture screens, and reuse authenticated sessions without consent, while Anthropic faces EU regulatory scrutiny for potentially breaching the ePrivacy Directive; the pre‑authorized manifest also widens the attack surface for prompt‑injection exploits that affect up to 23.6 % of prompts without mitigations.
