Security firm SquareX exposed a significant vulnerability in the OAuth implementation of Google Chrome extensions just days before a major breach occurred. The flaw allowed malicious actors to inject harmful code into extensions using a sophisticated phishing campaign. This campaign involved emails disguised as Chrome Store notifications regarding policy violations, prompting developers to connect their Google account to a fake "Privacy Policy Extension". This fake extension, in turn, granted attackers the ability to edit, update, and publish extensions on the developer's account, effectively hijacking them.
The identified attack vector was demonstrated by SquareX researchers in a video just before a malicious version of Cyberhaven’s browser extension was found on the Chrome store. This malicious extension was available for over 30 hours and affected over 400,000 users before it was removed by Cyberhaven. The incident highlights the increasing risk that browser extensions pose, as most organizations don't monitor what extensions their employees are using, making them a common target for cybercriminals.