Cyble threat intelligence researchers discovered a GitHub repository posing as a hiring coding challenge, tricking developers into downloading a backdoor that steals private data. The campaign employs a variety of novel approaches, including leveraging a social media profile for command and control (C&C) activities rather than C&C servers. Cyble Research and Intelligence Labs (CRIL) researchers discovered invoice-themed lures, suggesting that the campaign may be moving beyond a fake hiring challenge for developers.
According to a blog post by Cyble researchers,
the campaign appears to target Polish-speaking developers, and the malware exploits geofencing to restrict execution. The researchers believed that the campaign is disseminated through career sites such as LinkedIn or regional development forums.
The fake recruitment test, dubbed "FizzBuzz," dupes users into downloading an ISO file containing a JavaScript exercise and a malicious LNK shortcut. When executed, the LNK file ("README.lnk") invokes a PowerShell script that installs a stealthy backdoor known as "FogDoor" by the researchers.
Instead of employing C&C servers, FogDoor communicates with a social media platform using a Dead Drop Resolver (DDR) mechanism to retrieve attack directives from a profile, according to the researchers. The malware employs geofencing to limit execution to Polish victims.
When it becomes operational, "it systematically steals browser cookies, Wi-Fi credentials, and system data, staging them for exfiltration before deleting traces," Cyble told reporters. The malware employs remote debugging to collect Chrome cookies and can work in the background, while Firefox credentials are obtained from profile directories.
PowerShell script establishes persistence
The PowerShell script also opens a "README.txt" file "to trick consumers into believing they are interacting with a harmless file," Cyble stated. This paper includes instructions for a code bug patch task, "making it appear innocuous while ensuring the PowerShell script executes only once on the victim's machine to carry out malicious activities."
The PowerShell script also downloads an executable file and saves it as "SkyWatchWeather.exe" in the "C:\Users\Public\Downloads" folder. It then creates a scheduled task called "Weather Widget," which executes the downloaded file using mshta.exe and VBScript and is set to run every two minutes indefinitely.
SkyWatchWeather.exe serves as a backdoor by utilising a social networking platform (bark.lgbt) and a temporary webhook service (webhookbin.net) as its command and control infrastructure. After authenticating its location, the malware attempts to connect to "bark.lgbt/api" in order to get further orders embedded in a social media platform's profile information. Cyble added that this setup complicates identification and removal operations.