Security Experts:

New Windows Backdoor Linked to SambaCry Linux Malware

The cybercriminals who had recently delivered a cryptocurrency miner to Linux servers by exploiting the Samba vulnerability known as EternalRed and SambaCry are believed to have developed a backdoor designed for Windows systems.

The new malware, detected by Kaspersky Lab products as Backdoor.Win32.CowerSnail, uses the same command and control (C&C) server as the Linux malware, namely

CowerSnail was created using Qt, a cross-platform development framework. Experts believe its authors may have leveraged Qt in order to directly transfer Unix code instead of having to learn using the Windows API. On the other hand, while it does make it easier to transfer code between platforms, Qt significantly increases the size of the resulting file.

Once it infects the system, the malware escalates the priority of its process and starts communicating with its C&C server through the IRC protocol.

CowerSnail can collect information about the compromised machine, receive updates, execute commands, install or uninstall itself as a service, and receive updates.

After it harvests system information and sends it back to the C&C domain, the malware exchanges pings with the server and waits for commands from the attackers.

“After creating two separate Trojans, each designed for a specific platform and each with its own peculiarities, it is highly probable that this group will produce more malware in the future,” explained Kaspersky’s Sergey Yunakovsky.

The SambaCry vulnerability exploited by the Linux malware linked to this threat actor, CVE-2017-7494, can be exploited to upload a shared library to a writable share and cause the server to load that library. This allows a remote attacker to execute arbitrary code on the targeted system.

The security hole, patched in May, affects the products of several vendors, including routers and network-attached storage (NAS) appliances. In fact, one piece of malware spotted by Trend Micro in early July leverages the SambaCry vulnerability to target NAS devices, particularly ones used by small and medium-size businesses.

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.