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New Remaiten Malware Builds Botnet of Linux-Based Routers

Remaiten Linux Bot Targets Routers and Potentially Other Embedded (IoT) Devices

A new piece of malware is targeting embedded systems with the mission to compromise and make them part of a botnet, ESET security researchers have discovered.

Dubbed “Remaiten” (Linux/ Remaiten), the new threat combines the capabilities of previously spotted Tsunami (also known as Kaiten) and Gafgyt malware and also brings a series of improvements and new features. According to ESET, three versions of Remaiten have already emerged, while the malware authors call their creation “KTN-Remastered” or “KTN-RM.”

One of the capabilities that Remaiten borrows from Gafgyt is telnet scanning, though Remaiten enjoys a series of improvements, ESET’s Michal Malik explains in a blog post. Both, however, rely on improperly secured devices to successfully infect them.

Gafgyt attempts to connect to random routers via port 23, which it then issues a shell command to download bot executables for multiple architectures and tries to run them. Remaiten, on the other hand, carries downloaders for CPU architectures commonly used in embedded Linux devices, then tries to trigger the device’s platform to drop only the appropriate downloader.

When executed, the bot runs in the background and changes its process name to look legitimate, with two versions using “-bash” for that (namely Remaiten 2.0 and 2.1), and the third (version 2.2) using “-sh.” Next, using the create_daemon function, the bot creates a file named “.kpid” in one of the predefined daemon directories and writes its PID to a file.

The bot binaries include a hardcoded list of C&C server IP addresses, and the malware chooses one at random and connects to it on a hardcoded port (the port is different from one variant to another). Upon successful connection to the C&C server, the bot checks-in on the IRC channel, and the server replies with a welcome message and further instructions.

There are various IRC commands that the bot supports, one of which is “PRIVMSG,” used to instruct the bot to perform nefarious operations such as flooding, downloading files, and telnet scanning. According to ESET researchers, most of these capabilities come from the Linux/Tsunami malware, while the rest were borrowed from Linux/Gafgyt.

The bot sends to the C&C server information such as device’s IP address, the successful username and password pair, and whether it infected the other device or not. The malware also supports a “KILLBOTS” command, which allows it to enumerate running processes and kill some of them based on a few criteria, mainly because of their names.

Researchers also discovered that Remaiten version 2.2 includes a wget/tftp command to download a shell script that downloads the bot binaries, including files that target platforms such as PowerPC and SuperH. This proves that bad actors are ready for any situation, as they went into the trouble of compiling their malware for these architectures.

Additional technical details are available from ESET.

Related: Tens of Thousands of Routers, IP Cams Infected by Vigilante Malware

Related: Large DDoS Botnet Powered by Routers Infected With “Spike” Malware

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