Android Botnet leverages ADB ports and SSH to spread

Trend Micro recently discovered an Android crypto-currency mining botnet that can spread via open ADB (Android Debug Bridge) ports and Secure Shell (SSH).

Security researchers at Trend Micro have discovered an new Android crypto-currency mining botnet that spreads via open ADB (Android Debug Bridge) ports and Secure Shell (SSH). 

The Android Debug Bridge (adb) is a command-line tool that allows developers to communicate with an Android device. The adb command facilitates a variety of device actions, such as installing and debugging apps, and it provides access to a Unix shell that you can use to run a variety of commands on a device.

The ADB could be abused by malware to target Android phones through the port 5555. By default, Android has Android Debug Bridge (ADB) option disabled, but often vendors enable it to customize the operating system, then ship the devices with the feature turned on. In September 2018, researchers observed the Hide and Seek (HNS) IoT botnet targeting Android devices with ADB option enabled

“We observed a new cryptocurrency-mining botnet malware that arrives via open ADB (Android Debug Bridge) ports and can spread via SSH. This attack takes advantage of the way open ADB ports don’t have authentication by default, similar to the Satori botnet variant we previously reported.” reads the analysis published by Trend Micro. “This bot’s design allows it to spread from the infected host to any system that has had a previous SSH connection with the host.”

The botnet spotted by Trend Micro is also able to spread to systems that were previously connected to it via SSH. 

Tha attack is originated from the IP address 45[.]67[.]14[.]179 that connects to the ADB running device or system and attempt to conduct several activities. Initially, it changes the working directory to “/data/local/tmp,” because files stored there typically have default permission to execute.

The malicious code attempt to determine if it is running in a honeypot, then it downloads the payload and changes its permission settings to allow its execution.

The script for a.sh reveals shows that the attackers can choose from three different miners. In order to determine what miner to deliver, the bot collects system information, such as manufacturer, hardware details, and processor architecture. 

The script also enhances the victim’s memory by enabling HugePages, in this way the system would support memory pages that are greater than its default size.   The bot also attempts to lock out other threats by modifying /etc/hosts.

“This botnet malware also tries to block its competitor by modifying /etc/hosts. By adding the additional record  “0.0.0.0 miningv2.duckdns.org”, it blocks the URL of the competing miner. It also kills that competitor’s process with the command “pkill -9 r32”.” continues the analysis.

The malicious code also implements an evasion technique that involves deleting the downloaded files and removing the traces on the victim host.

The bot attempts to spread to any device that has previously connected to the victim via SSH. Usually, these devices are included in a “known” list of systems and allow communication without requiring further authentication after the initial key exchange. 

The bot leverages two spreaders to infect systems from the “known” list via SSH, they only differ for the directories used to search “known_hosts”.   

The Android-botnet already infected devices in 21 different countries, most of them in South Korea.

“Although ADB is a useful feature for administrators and developers, it is important to remember that an enabled ADB might expose the device and those connected to it to threats.” concludes Trend Micro.

“Users can also follow other best practices for defending against illicit cryptocurrency-mining activities and botnets, such as:

• Checking and changing default settings when necessary to increase security
• Updating device firmware and applying available patches
• Being aware of methods attackers use to spread these types of malware and tailoring defenses against them”

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Pierluigi Paganini

(SecurityAffairs – Android, botnet)

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