The Sophos Managed Threat Response (MTR) team and SophosLabs researchers have been investigating an ongoing ransomware campaign from Russian threat actors called Snatch for about a year. It was highly targeted to high-payout victims, and seemed the work of financially oriented attackers.
But things just got uglier recently. Sophos realized that the malware had changed how it was doing things.
The victim’s PC was being rebooted into the Safe Mode of Windows before the encryption of data files was being done. It is both a novel and evil technique, as Andrew Brandt (the author of the Sophos blog report) said on Twitter.
Running the encryption in Safe Mode means that endpoint protection software that may be present will not operate. Even AV software is cut off. The victim’s defensive line is totally swamped by this method.
Fortunately Snatch is not multi-platform, even though it was coded in Go, Google’s multi-platform coding language. Sophos says that, “the malware we’ve observed isn’t capable of running on platforms other than Windows. Snatch can run on most common versions of Windows, from 7 through 10, in 32- and 64-bit versions.”
Sophos thinks that Snatch’s operators have adopted the “active automated attack” model, in which they seek to penetrate enterprise networks via automated brute-force attacks against vulnerable, exposed services, and then leverage that foothold to spread internally within the targeted organization’s network through human-directed action.
They got the needed partners by advertising on criminal message boards. Sophos found one of the “Snatch Team” posting a quite explicit ad saying they were “Looking for affiliate partners with access to RDP\VNC\TeamViewer\WebShell\SQL inj [SQL injection] in corporate networks, stores and other companies.”
Sophos found that in one case, attackers initially accessed the company’s internal network by brute-forcing the password to an administrator’s account on a Microsoft Azure server, and were able to log in to the server using Remote Desktop (RDP). They could then conduct surveillance of the network which lasted weeks.
The ransomware installs itself as a Windows service called SuperBackupMan, which has properties that prevent it from being stopped or paused by the user while it’s running. The malware then adds this key to the Windows registry so it will start up during a Safe Mode boot.
Using the BCDEDIT tool on Windows, it issues a command that sets up Windows in Safe Mode, and then immediately forces a reboot of the infected computer.
Sophos recommends that “organizations of any size refrain from exposing the Remote Desktop interface to the unprotected internet. Organizations that wish to permit remote access to machines should put them behind a VPN on their network.”
They also say that organizations should immediately implement multi-factor authentication for users with administrative privileges, to make it more difficult for attackers to brute force those account credentials.
— Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other things, a consulting editor for BYTE magazine and senior editor for the launch of WebWeek.