SquareX and Perplexity Quarrel Over Alleged Comet Browser Vulnerability

SquareX claims to have discovered a potentially critical vulnerability in Perplexity’s Comet AI browser centred on a limited-documentation Model Context Protocol API and two hidden extensions, which allegedly can be abused to execute local commands. Perplexity has dismissed the research as fake security work, saying it has implemented measures to prevent the attack but that the scenario is contrived.

In a demonstration, SquareX showed an attack technique called “extension stomping” that impersonates the legitimate Comet analytics extension and sideloads a malicious one, allegedly enabling ransomware deployment. The firm said it reported its findings to Perplexity on 4 November, but Perplexity had not responded by the time of disclosure.

Perplexity claimed there are user-consent requirements for local MCP actions and that no known attacks have targeted Comet users, while noting it does work with researchers to identify and patch potential vulnerabilities. SquareX acknowledged that some attack vectors would require less user interaction than the demonstrated method, though it stressed the MCP API permissions and risks remain a concern.