The malware, dubbed SHARPEXT by researchers from security firm Volexity, uses clever means to install a browser extension for the Chrome and Edge browsers, Volexity reported in a blog post. The extension can’t be detected by the email services, and since the browser has already been authenticated using any multifactor authentication protections in place, this increasingly popular security measure plays no role in reining in the account compromise. The extension isn’t available in Google’s Chrome Web Store, Microsoft’s add-ons page, or any other known third-party source and doesn’t rely on flaws in Gmail or AOL Mail to get installed.
Volexity President Steven Adair said in an email that the extension gets installed “by way of spear phishing and social engineering where the victim is fooled into opening a malicious document.