OBSCURE MCP API IN COMET BROWSER BREACHES USER TRUST, ENABLING FULL DEVICE CONTROL VIA AI BROWSERS

Summary from the TLDR InfoSec newsletter

SquareX researchers exposed a hidden MCP API (chrome.perplexity.mcp.addStdioServer) in the Comet browser that enables embedded extensions to execute arbitrary local commands without user consent, thereby bypassing decades of established browser security principles. The API is accessible via Comet's Agentic extension, triggered by perplexity.ai, creating a catastrophic third-party risk where a single XSS vulnerability or a compromised Perplexity employee could grant attackers complete device control over all Comet users. Security teams should audit AI browser deployments, demand API disclosure from vendors, require third-party security audits, and ensure users can disable embedded extensions that are currently hidden from extension dashboards.