Recently, a team of cybersecurity researchers from CrowdStrike has exposed a malvertising campaign that targeted AnyDesk. Malvertising has been around for a while alluring users to install the malware in their system. This time researchers flagged a “clever” malvertising campaign, delivering weaponized AnyDesk installer through targeted Google ad that displayed in the search engine results page for the keyword “anydesk.”
According to the CrowdStrike Falcon Complete team, the campaign is believed to have started off as early as April 21, 2021.
It involved a malicious file that pretences as an executable setup for AnyDesk called “AnyDeskSetup.exe”. Upon execution, it exhibits suspicious behavior that did not seem to be the legitimate AnyDesk Remote Desktop application. Being weaponized with additional capabilities the above setup downloads a PowerShell implant to infiltrate and collect information from the system.
“The initial detection kicked off an internal collaboration across CrowdStrike’s Falcon OverWatch™ threat hunting, Intelligence, and Threat Detection and Response teams to piece everything together and respond to this emerging activity across the CrowdStrike customer base,” CrowdStrike mentioned in its blog post.
During the analysis of the suspected setup file, a remote connection with the affected host was made using Falcon Real Time Response (RTR) to collect additional insights into the detection. It let the researcher capture and acquire a copy of the PowerShell script “v.ps1”, observed initially.
“The script had some obfuscation and multiple functions that resembled an implant as well as a hardcoded domain (zoomstatistic[.]com) to ‘POST’ reconnaissance information such as user name, hostname, operating system, IP address and the current process name. In addition to the hardcoded domain, the script also had a specific user-agent string and URI to connect to,” researchers from CrowdStrike said in an analysis released in the blog.
The investigating team found logic in the PowerShell script very similar to that observed and published by Inde, where impersonated Zoom installer dropped a similar PowerShell script through an external resource.
With the script findings, initially, the research team believed the delivery mechanism to be a phishing or social engineering attempt. Later at a certain point, the attack throws a curve at the intrusion route, signaling that it is beyond an ordinary data-gathering operation. So the investigation was turned to Endpoint Activity Monitoring (EAM) to gain further context and determine the origin of the activity.
While investigating a detection apparently dropping from a Setup or Installer file, the team proceeded with the first step to understand how that installer was written to disk. After probing Falcon endpoint detection and response (EDR) data, they made it to discover the origin of the activity. The malicious Google ad placed by the threat actor distributed the suspicious AnyDesk installer, which served to unsuspicious users who searched for ‘AnyDesk’ on Google.
“The DnsRequests and PeFileWritten via Google Chrome confirmed our suspicion that the activity started with a user-initiated download, but when diving deeper to investigate the cause, we made a fascinating finding in the user’s web traffic: The user had been attempting to search for “AnyDesk” using Google Chrome and was served up a malicious advertisement that forced a redirect to domohop[.]com, leading to the trojanized version of AnyDesk,” reported CrowdStrike.
However, the cybersecurity firm did not name any specific threat actor or nexus for this fraudulent cyber activity. It, in fact, suspected the activity to be a “widespread campaign affecting a wide range of customers” given the large user base. According to the company’s website, more than 300 million users across the world downloaded AnyDesk’s remote desktop access solution.
The Falcon Complete team working on this investigation further, looked for additional compromises and a way to contain the threat. The CrowdStrike wrote, “Once the Falcon Complete team had determined the initial access vector and the extent of the compromise, and had fully remediated the first host, the next step in the scoping process was to search across our customer base and identify additional compromises. By performing a hunt using a combination of network and host-based indicators of attack, the Falcon OverWatch team was able to identify additional customers impacted by the same activity. Falcon Complete was then able to follow the same analysis and remediation process for each of our Falcon Complete customers to contain the threat.”
An estimated data from CrowdStrike indicated that 40% of clicks on the malicious ad in Google search turned into installations of the AnyDesk binary, and 20% of those installations included follow-on hands-on-keyboard activity. “While it is unknown what percentage of Google searches for AnyDesk resulted in clicks on the ad, a 40% Trojan installation rate from an ad click shows that this is an extremely successful method of gaining remote access across a wide range of potential targets,” the researchers said.
After discovering trojanized AnyDesk installer, the company reportedly notified Google of its findings, which is said to have taken instantaneous action to remove the ad in question.
“This malicious use of Google Ads is an effective and clever way to get mass deployment of shells, as it provides the threat actor with the ability to freely pick and choose their target(s) of interest,” said the researchers.
“Because of the nature of the Google advertising platform, it can provide a really good estimate of how many people will click on the ad. From that, the threat actor can adequately plan and budget based on this information. In addition to targeting tools like AnyDesk or other administrative tools, the threat actor can target privileged/administrative users in a unique way,” CrowdStrike concluded.