Researchers at Zscaler have conducted an analysis of some of the most prevalent IRC-based botnets and determined that these types of threats remain effective as the features incorporated into them continue to improve.
IRC botnets rely on IRC servers for command and control (C&C) communications. Their operators control malware-infected machines through IRC channels.
One of the most prevalent IRC-based botnets is powered by Dorkbot (also known as Nrgbot), a worm capable of stealing passwords, enlisting infected devices in distributed denial-of-service (DDoS) attacks, downloading other pieces of malware, and preventing users from downloading security updates. The threat is distributed via USB drives, social media websites, and instant messaging services.
Over the last three months, Zscaler has been monitoring one of the domains used to serve the Dorkbot installer. Once it infects a device, the malware creates a registry entry for persistence and starts injecting threads into processes such as svchost.exe, mspaint.exe, and calc.exe.
The thread injected into mspaint.exe is designed to resolve a list of domains, while the thread in the calc.exe process is used to download additional malware from a total of 20 URLs encrypted using a custom encryption method. Researchers also noted that Dorkbot has a user-mode rootkit component.
In addition to Dorkbot, Zscaler has also analyzed three other IRC bot families: RageBot, Phorpiex, and IRCBot.HI. According to the security firm, these worms are designed to check for the presence of a virtual machine, sandbox or honeypot in an effort to prevent researchers from analyzing them.
Each of these threats has a different propagation mechanism. RageBot spreads by copying itself into RAR archive files, and folders associated with instant messaging and peer-to-peer (P2P) applications. Phorpiex spreads through removable drives, while the IRCBot.HI sample analyzed by Zscalers was designed to leverage Skype in order to spread.
Once they infect a machine, RageBot, Phorpiex, and IRCBot.HI start communicating with their IRC-based C&C servers from which they receive instructions on what activities to carry out.
“In this era of sophisticated Botnets with multiple C&C communication channels, custom protocols, and encrypted communication; we continue to see a steady number of new IRC based Botnet payloads being pushed out in the wild on a regular basis.” Zscaler researchers noted in a blog post. “As we saw in our analysis, IRC based Botnet families continue to evolve in terms of sophisticated features incorporated in the bots.”