A newly identified malvertising campaign has been discovered, employing an in-browser simulation of a Windows update to distribute the Aurora information stealing malware. Aurora, a Golang-based malware, has been circulating on hacker forums for over a year, boasting extensive capabilities and evading antivirus detection.
Researchers at Malwarebytes found that the campaign relied on popunder ads on high-traffic adult content websites, redirecting unsuspecting users to a location serving the malware. Despite a relatively low impact, with approximately 30,000 users redirected and nearly 600 installations of the data-stealing malware, the campaign highlights the constant efforts of threat actors to develop undetectable tools.
The malvertising operation utilized popunder ads, a type of inexpensive pop-up ad that launches behind the active browser window, remaining hidden until the user closes or moves the main browser window. While a previous campaign in December had significant impact, amassing hundreds of thousands of visitors and fraudulent ad impressions, the more recent one identified by Malwarebytes had a lower reach.
The attackers devised an inventive approach where the popunder displayed a full-screen browser window mimicking a Windows system update screen, deceiving users into thinking they were installing legitimate updates.
The researchers at Malwarebytes tracked numerous domains used in the campaign, many of which impersonated adult websites. These domains, including activessd[.]ru, oled8kultra[.]ru, and click7adilla[.]ru, simulated the fake Windows update and prompted users to download a file named “ChromeUpdate.exe.” Despite the deceptive nature of the full-screen browser screen, some users were still tricked into running the malicious executable and falling victim to the attack.
The alleged Chrome updater, dubbed ‘Invalid Printer,’ served as a “fully undetectable” (FUD) malware loader exclusive to this particular threat actor. When initially discovered by Malwarebytes, no antivirus engines on Virus Total flagged it as malicious.
However, detection gradually increased after the publication of a relevant report from Morphisec. ‘Invalid Printer’ checks the graphic card of the host system to determine if it is running in a virtual machine or sandbox environment. If it passes the check, the loader unpacks and launches the Aurora info stealer, emphasizing the threat actor’s focus on creating evasive tools.
Further investigation revealed the use of an Amadey panel, suggesting the involvement of a well-documented reconnaissance and malware loading tool, as well as the targeting of Ukrainians through tech support scams.
Malwarebytes provides a detailed technical analysis of the malware’s installation and behavior, along with indicators of compromise that organizations and security vendors can utilize to protect their users from such threats.
