Researchers Analyze Multipurpose Malware Targeting Linux/Unix Web Servers

An in-depth analysis of a recently discovered piece of malware that’s designed to target Linux and Unix Web servers has been published on Thursday by Virus Bulletin.

Andrew Kovalev, Konstantin Otrashkevich and Evgeny Sidorov, researchers at the Russian Internet company Yandex, have studied both the client side and the command and control (C&C) servers of the malware dubbed “Mayhem.”

 Mayhem, a partial analysis which was published in May by the MalwareMustDie research group, is a multipurpose modular threat that has the functions of a traditional Windows bot, but which can operate even under restricted system privileges, the Russian experts said.

According to the researchers, the threat is distributed as a PHP script, which in mid-June was detected by only three of the antivirus engines on VirusTotal. After infecting a system, Mayhem begins communicating with its command and control (C&C) server via HTTP POST requests and responses.

A total of seven C&C commands have been identified. The malware can inform the server that it has been successfully loaded, it can request files, it can send data, and provide a report on its state. Additioanlly, the C&C can command the bot to run a new task, load a plugin, send data, and stop the current task, the research paper reveals.

 Mayhem also relies on plugins, which are stored in a hidden file system just like the rest of the malware files, to perform a wide range of tasks. Researchers identified a total of eight plugins in the wild that can be used to find vulnerable websites, conduct brute-force attacks on various types of sites and accounts, and extract useful information from Web pages. In addition to these eight, there are a number of plugins that haven’t been seen in the wild, including one designed to exploit the Heartbleed vulnerability.

By gaining access to two C&C servers, experts have determined that at least 1,400 servers have been infected with this threat, most of them being located in the United States, Russia, Germany and Canada.

Kovalev, Otrashkevich and Sidorov believe that Mayhem is actually the continuation of Fort Disco, a major brute-force campaign detailed in the summer of 2013 by Arbor Networks.

 Several pieces of malware designed to target Linux and Unix systems have been developed over the past period. In March, Symantec revealed the existence of a Linux worm capable of helping cybercriminals use compromised computers to mine for crypto-currencies. Earlier this month, Kaspersky Lab reported uncovering a Linux Trojan with DDoS functionality.

The complete paper on Mayhem is available on Virus Bulletin.