Pierluigi Paganini December 06, 2021

Experts spotted a series of malvertising campaigns using fake installers of popular apps and games to deliver a backdoor and a malicious Chrome extension.

Talos researchers spotted a series of malvertising campaigns using fake installers of popular apps and games as a lure to trick users into downloading a new backdoor and an undocumented malicious Google Chrome extension.

According to Talos, the threat actor has been active at least since late 2018, experts observed intermittent activity towards the end of 2019 and through early 2020. The group resurfaced in April 2021, the malvertising campaigns targeted users in Canada, the U.S., Australia, Italy, Spain, and Norway.

Upon executing the fake installers, they execute the following pieces of malware on the victim’s system:

• A password stealer called RedLine Stealer.
• An AutoIt-based backdoor used to establish a remote access via a stealth Microsoft Remote Desktop session by forwarding the RDP port through an SSH tunnel. The backdoor allows access to infected systems, even when behind a firewall.
• A malicious browser extension, dubbed MagnatExtension, that contains several information-stealing features, such as keylogging and taking screenshots.

“The attack begins when a victim looks for a particular piece of software for download. Talos believes the attacker has set up an advertising campaign that will present links to a web page, offering the download of a software installer. The installer has many different file names. For example: viber-25164.exe, wechat-35355.exe, build_9.716-6032.exe, setup_164335.exe, nox_setup_55606.exe and battlefieldsetup_76522.exe.” reads the post published by Talos. “When executed, this installer does not install the actual software it announces, but instead executes a malicious loader on the system.”

Cisco Talos researchers attributed the campaigns to an unknown threat actor tracked as “magnat.” The experts noticed that the group is reportedly updating the malware families.

The MagnatExtension, which masquerades as Google’s Safe browsing, allows attackers to steal form data, harvest cookies, and also execute arbitrary JavaScript code on the victim’s system.

The C2 address used by the extension is hardcoded, it can be updated by the current C2 with a list of additional C2 domains. The attackers also implemented a backup mechanism for C2, that allows to obtain a new C2 address from a Twitter search for hashtags like “#aquamamba2019” or “#ololo2019.”

The algorithm for getting the domain from the tweet is simple as effective, it concatenates the first letter of each word of the content of a tweet. The tweet “Squishy turbulent areas terminate active round engines after dank years. Industrial creepy units” that contains the hashtag “#aquamamba2019” is translated to “stataready[.]icu.”

Once an active C2 is available, the data are sent in json format in the body of an HTTP POST request. The json string is encrypted.

“Based on the use of password stealers and a Chrome extension that is similar to a banking trojan, we assess that the attacker’s goals are to obtain user credentials, possibly for sale or for his own use in further exploitation,” concludes Cisco Talos. “The motive for the deployment of an RDP backdoor is unclear. The most likely are the sale of RDP access, the use of RDP to work around online service security features based on IP address or other endpoint installed tools or the use of RDP for further exploitation on systems that appear interesting to the attacker.”

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Pierluigi Paganini

(SecurityAffairs – hacking, malvertising)

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