New Malware Targeting Linux and Unix Nginx Web Servers

New malware targeting Linux and Unix Nginx web servers, malware authors not only make user of far better network connections and more powerful servers than the average Windows PC, servers are also less likely to be updated on a regular basis and they are less likely to run security software.

VirusBtn published a paper by three of the aforementioned Yandex researchers in which they analyse 'Mayhem', a new kind of malware that runs on *nix servers and is able to gain maximum benefits, even when running under restricted privileges on the target system.

The malware has been designed to conduct various types of DDoS attacks against the servers specified.

Kaspersky Lab products detect it as Backdoor.Linux.Mayday.f. The files kysapdd, skysapdd, xfsdxd, ksapdd are almost exact copies of atddd - with one exception, which is discussed later in the text.

The backdoor starts its operation by calling the function daemon(1, 0), continuing to run in the background and redirecting standard input, output and errors to /dev/null

Next, atddd collects relevant information about the system, including:

1. system version (by calling uname())
2. number of CPU cores and their clock rates (taken from /proc/cpuinfo)
3. CPU load (taken from /proc/stat)
4. network load (data for interfaces with the "eth" prefix taken from /proc/net/dev)

The information listed above is stored in the g_statBase structure.

The backdoor decrypts strings defining the C&C server's IP address and port number. The encryption algorithm used is very simple: an encrypted string is taken character-by-character, with 1 added to the ASCII code of a character if its number is odd and subtracted from it if the character's number is even. 

Atddd reads configuration file fwke.cfg, which is located in the same folder with the malicious program. Information from the config file is saved in the g_fakeCfg structure. If the file does not exist.

Mayhem, a partial analysis of which was previously published by Malware Must Die!, infects a server via PHP script. Once installed, the malware runs in an infinite loop and uses HTTP POST to send information to and receive instructions from a command and control server. 

The core functionality of the malware is determined by a number of plug-ins, which are stored in a hidden file system. Most of the plug-ins help those controlling the malware find other web servers to infect, either by looking for vulnerabilities or by using brute force to gain access.

The researchers also managed to gain access to two command and control servers. This allowed them to determine that the malware had infected at least 1,400 servers, most of which are located in the USA, Russia, Germany and Canada. 

They also found a number of plug-ins that have yet to be seen in the wild, including one that exploits the Heartbleed vulnerability in OpenSSL




Author Venkatesh Yalagandula Follow us Google + and Facebook and Twitter