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Fake Chrome Font Update Attack Distributes Backdoor

A malicious campaign targeting users of the Chrome web browser on Windows systems recently started distributing a remote access Trojan, security researchers have discovered.

A malicious campaign targeting users of the Chrome web browser on Windows systems recently started distributing a remote access Trojan, security researchers have discovered.

First spotted in December 2016, the attack is tied to the EITest compromise chain, and has been observed distributing the Fleercivet ad fraud malware and ransomware variants such as Spora and Mole. Initially targeting only Chrome, the campaign was expanded earlier this year to target Firefox users as well.

The attack relies on pop-ups being displayed in the Chrome browser on Windows devices, claiming that users need to install a so called HoeflerText font pack. Code injected into compromised websites would make the visited pages look unreadable, thus making the fake popup seem legitimate.

Fingerprinting capabilities included in the injected code trigger the attack if certain criteria are met (targeted country, correct User-Agent (Chrome on Windows) and proper referer). If the social engineering scheme is successful and the user accepts to install the fake font pack, a file named Font_Chrome.exe is downloaded and executed, and their system is infected with malware.

Starting in late August, the malware distributed via these fake Chrome font update notifications is the NetSupport Manager remote access tool (RAT). According to Palo Alto Networks’ Brad Duncan, this should indicate “a potential shift in the motives of this adversary.”

“Network traffic follows two distinct paths. Victims who use Microsoft Internet Explorer as their web browser will get a fake anti-virus alert with a phone number for a tech support scam. Victims using Google Chrome as their browser will get a fake HoeflerText popup […] that offers malware disguised as Font_Chrome.exe,” Duncan explains.

The most recent versions of Font_Chrome.exe are represented by file downloaders designed to retrieve a follow-up malware that would install NetSupport Manager. This commercially-available RAT was previously associated with a campaign from hacked Steam accounts last year.

While analyzing the recent attack, Palo Alto’s researchers discovered two variants of the file downloader and two instances of follow-up malware to install the RAT. Although the RAT is already at version 12.5, the version Chrome users are targeted with is at version 11.0, the researchers discovered.

Chrome users on Windows systems should be suspicious of any popup messages that inform them the “HoeflerText” font wasn’t found. Affected users aren’t expected to notice a difference in their system’s operation, given that this is a backdoor program, but that doesn’t mean they weren’t compromised.

“It’s yet to be determined why EITest HoeflerText popups changed from pushing ransomware to pushing a RAT. Ransomware is still a serious threat, and it remains the largest category of malware we see on a daily basis from mass-distribution campaigns. However, we have also noticed an increasing amount of other forms of malware in recent campaigns, especially compared to 2016,” Duncan notes.

He also points out that RATs give attackers more capabilities on an infected host and also provide more flexibility compared with malware that has been designed for a single purpose, and that the recently observed change in the EITest HoeflerText popups might suggest that ransomware is slightly less prominent than it once was.

Related: Fake Chrome Font Update Attack Distributes Ransomware

Related: Backdoored RAT Builder Kit Offered for Free

Written By

Ionut Arghire is an international correspondent for SecurityWeek.

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