Perplexity's AI-powered browser, Comet, was found to have a serious vulnerability that could have exposed sensitive user data through indirect prompt injection, according to researchers at Brave, a rival browser company.

The flaw stemmed from how Comet handled webpage-summarisation requests. By embedding hidden instructions on websites, attackers could trick the browser's large language model into executing unintended actions, such as extracting personal emails or accessing saved passwords.

Brave researchers demonstrated how the exploit could bypass traditional protections, such as the same-origin policy, showing scenarios where attackers gained access to Gmail or banking data by manipulating Comet into following malicious cues.

Brave disclosed the vulnerability to Perplexity on 11 August, but stated that it remained unfixed when they published their findings on 20 August. Perplexity later confirmed to CNET that the flaw had been patched, and Brave was credited for working with them to resolve it.