The rogue extensions are advertised on Facebook by scammers and claim to allow changing the color of profile pages, tracking profile visitors or even removing social media viruses, said Kaspersky Lab expert Fabio Assolini in a blog post on Friday.
Assolini has recently observed an increase in the number of Facebook scams that use malicious Chrome extensions and originate in Brazil.
Once installed in the browser, these extensions give attackers complete control over the victim’s Facebook account and can be used to spam their friends or to Like pages without authorization.
In one case, a rogue extension masqueraded as Adobe Flash Player and was hosted on the official Chrome Web Store, Assolini said. By the time it was identified, it had already been installed by 923 users.
“We reported this malicious extension to Google and they removed it quickly,” Assolini said. “But we noted the bad guys behind this malicious scheme are uploading new extensions regularly, in a cat and mouse game.”
Uploading multiple rogue extensions on the Chrome Web Store and running several Facebook spam campaigns to advertise them allows attackers to quickly compromise thousands of accounts.
The accounts are then used to earn scammers money by Liking particular pages. The people behind these campaigns sell packages of 1, 10, 50 or 100 thousand Likes to companies who wish to gain visibility on Facebook.
The use of Trojan horse browser extensions to hijack accounts is not new, nor is the method specific to Google Chrome. However, it has several advantages over other techniques. For one, users are more likely to trust an extension distributed from the official Chrome Web Store for Chrome, or Mozilla’s add-on repository for Firefox, than a clickjacking or phishing page. Few users are aware that browser extensions can intercept everything they do through the browser.
Security compromises based on rogue browser extensions are also more persistent than those based on password theft or other methods, because these extensions can piggyback on active sessions to perform unauthorized actions even if the account owners change their passwords or enable two-factor authentication.
“Think twice before installing a Google Chrome extension,” Assolini said.