The latest variant of the GandCrab ransomware breaks infected Windows 7 systems, Fortinet warns.
Discovered at the end of last month, version 3 of the ransomware forces a system reboot, attempting to change the PC’s desktop wallpaper. Because of a coding bug, however, only Windows 10 and Windows 8 systems would fully load, while Windows 7 machines would hang at a point before the Windows Shell is completely loaded.
GandCrab spreads via spam emails, and Fortinet last week observed an uptick in messages distributing the ransomware. The emails carried version 2.1 of the malware and most of them (75%) targeted users in the United States, with those in the United Kingdom, Canada, Romania, and South Africa also impacted.
Over the past several days, the GandCrab operators switched to a new malware iteration, but kept most of the functionality intact. The main difference between the two versions is the attempt to change the desktop wallpaper, which only works on Windows 10 and Windows 8.1 systems.
“On Windows 7 however, for some reason, booting does not finish but instead gets stuck at a point before the Windows Shell is completely loaded. That means an infected user would not have the Windows interface to interact with, rendering the entire machine seemingly unusable,” Fortinet explains.
Reminiscent of the old lock screen ransomware behavior, the user sees only the ransom note wallpaper and TOR browser download site, the security researchers note.
This behavior, however, wasn’t intentional, it seems. The ransom note instructs the victim to read a copy of one of the “CRAB-DECRYPT.txt” ransom notes the malware has placed in various folders for instructions on how to recover the encrypted files. Without the Windows interface, the average user won’t be able to do that.
Users should launch Task Manager using the CTRL+SHIFT+DEL keys combination, terminate the malware process (which could also prove difficult to spot on the list of running processes) and reboot the system. However, this might not solve the issue either, given that the malware has a persistence mechanism that ensures it is executed upon reboot.
To prevent the “lock screen” from appearing in subsequent reboots, the victim should also delete the malware executable from APPDATA%Microsoft<random chars>.exe after terminating the malware process using Task Manager. Victims should also delete the ransomware’s autorun registry.
“Seeing a ransom note and realizing that all of your files are gone is frustrating on so many levels. And it’s even more frustrating (if that’s even possible) when on top of that you also lose your access to the machine. Malware flaws with unintended consequences are really quite common, which is another reason why being extra cautious with unsolicited emails is very important,” Fortinet notes.
Users are advised to always scan and verify unexpected emails with attachments before opening them. They should also create isolated backups of their important files, to ensure they can recover those in the event of an infection.
Although the new feature in GandCrab does not work well on all targeted systems, it is being actively deployed, which makes the malware campaign even more dangerous.