New Botnet Launches DDoS Attacks from Linux Computers

New Botnet Launches DDoS Attacks from Linux Computers

Researchers at SophosLabs have discovered a new botnet that launches a distributed denial-of-service (DDoS) attack from compromised Linux servers and IoT devices.

What is a DDoS Botnet? 

A botnet is a collection of computers compromised by a malicious software (malware) and controlled as a group without the owners' knowledge to conduct illegal activities, including DDoS attacks.

In a DDoS attack, hijacked or compromised computers are controlled as a group to attack a particular target, for instance, to overwhelm a particular website with traffic to render the site inaccessible to legitimate users. By leveraging the use of a botnet, attackers can carry out large-scale DDoS attacks. 

DDoS attacks don’t just target websites. They also target servers (web, email, DNS, file), web apps, banking, trading and e-commerce platforms, and VoIP systems.

Latest DDoS Botnet

SophosLabs researchers called the latest DDoS botnet that they’ve discovered “Chalubo”. The researchers said they first observed Chalubo in the wild in late August this year. On the 6th of September 2018, SophosLabs researchers said they first recorded how Chalubo works via a honeypot, a decoy computer system used in tracking new hacking methods.

According to the researchers, Chalubo attacks SSH servers, a software program used to remotely access Linux operating systems. There are currently a variety of Chalubo botnet versions for different processor architectures, including both 32- and 64-bit ARM, x86, x86_64, MIPS, MIPSEL and PowerPC.

Chalubo attackers gain access to a computer by using publicly known default and common username and password combinations. Once the attackers gain access to a computer, it issues commands that retrieve the Elknot, also known as Linux/BillGates malware, a notorious DDoS botnet family that runs on both Linux and Windows operating systems. Elknot, in turn, delivers the rest of the Chalubo botnet package.

This recently reported DDoS botnet incorporates the code of two other notorious DDoS botnets, the Mirai botnet and Xor.DDoS botnet.

In December last year, 3 college-age friends pleaded guilty for creating the Mirai botnet. According to the U.S. Department of Justice, the Mirai botnet, at its peak, consisted of hundreds of thousands of compromised IoT devices used to launch DDoS attacks.

Xor.DDoS botnet, meanwhile, was first observed in the wild in 2015. This botnet hijacks Linux computers for DDoS attacks. While Mirai uses 62 default username and password combinations to gain access to a computer or device, Xor.DDoS uses common or weak username and password combinations.

Chalubo, in particular, uses some of Mirai’s randomizing functions and what appears to be an extended form of the util_local_addr function. Chalubo also uses Xor.DDoS’ DelService & AddService functions, as well as Chalubo’s script gets dropped exactly in the same manner as Xor.DDoS. While Chalubo copies a few code snippets of Mirai and Xor.DDoS, it’s a different botnet taken as a whole, researchers at SophosLabs said.

“The majority of functional code in this bot is entirely new, with a focus on their own Lua handling for, primarily, performing DoS attacks with DNS, UDP, and SYN flavours,” SophosLabs researchers said. “The Lua script built into the bot is a basic control script for calling home to a C2 [command-and-control] server to inform the C2 about details of the infected machine.”

Chalubo’s Lua script communicates with the command-and-control server – a computer that’s controlled by attackers – to receive further instructions. The purpose of the script is to download, decrypt and then execute whatever the script finds.

Chalubo's main components, dropper (the Elknot), main bot and Lua script, are encrypted using the ChaCha stream cipher in an effort to prevent detection. SophosLabs researchers observed that Chalubo triggered the infected computer to conduct a DDoS attack against a single Chinese IP address over port 10100, without masking the local source IP.

According to SophosLabs researchers, the creator or creators of Chalubo botnet may be at the end of testing their botnet and we may see an increase in activity from this new botnet.

Prevention

A DDoS botnet negatively impacts the hijacked computers. In a similar manner, a DDoS attack negatively impacts a target.

Here are a few signs that the computer in your organization may be a part of a botnet:

-Computer fan kicks into overdrive even when it’s idle

-It takes a long time to shut down the computer or it won’t shut down properly

-Computer programs and internet access are slow

Here are some security measures to prevent attackers from turning the computers in your organization as part of the Chalubo, Mirai or Xor.DDoS botnets:

-Change default and common username and password combinations as these botnets hunt computers using default and common or weak username and password combinations

-In the case of the Chalubo botnet, use SSH keys instead of passwords for logins

-Keep all your software up-to-date

On the part of the DDoS botnet target, a successful DDoS attack against a website, server, e-commerce platform or VoIP system negatively impacts the target’s reputation and damages existing client relationships.

DDoS botnets can be prevented from attacking online resources by regularly monitoring traffic and by conducting a DDoS testing – called in the cybersecurity field as penetration or pen testing.

By monitoring the traffic of your organization’s online resources, abnormal and suspicious traffic can be flagged early on. In DDoS testing, simulated DDoS attacks are conducted against the online resources of your organization to check if they can withstand real DDoS attacks.

Contact ustoday if you need assistance in preventing attackers from hijacking your organization’s computers as part of a DDoS botnet or if you want assistance in protecting your organization’s online resources from DDoS attacks.