Linux Servers at Risk from REDXOR Malware

Most websites are hosted on Linux servers, and unfortunately, that platform is under siege by a new threat called RedXOR malware. 

What is Happening?

Threat researchers have discovered a backdoor attack being waged by a hacker group called Winnti. Legacy Linux systems are at risk of data exfiltration and intercepting network traffic and rerouting it to alternate locations. 

What is RedXOR Malware?

The RedXOR malware is named as such because it is based on the XOR encryption algorithm and affects an old version of the Red Hat Enterprise Linux platform. 

According to ThreatPost, “The initial compromise in this campaign is not known, but some common entry points to Linux environments are Use of compromised credentials or by exploiting a vulnerability or misconfiguration. It is also possible the initial compromise was via a different endpoint, meaning the threat actor laterally moved to a Linux machine where this malware was deployed.”

So far, only two victims have identified RedXOR in their environment. Samples were issued to VirusTotal from Indonesia and Taiwan. 

ThreatPost explains in detail how the malware works “After execution, RedXOR creates a hidden folder (called “.po1kitd.thumb”) inside a home folder, which is then utilized to store files related to the malware. Then, it creates a hidden file (“.po1kitd-2a4D53”) inside this folder. The malware then installs a binary to the hidden folder (called “.po1kitd-update-k”) and sets up persistence via “init” scripts.

The malware stores the configuration encrypted within the binary. In addition to the command-and-control (C2) IP address and port, it can also be configured to use a proxy. The configuration includes a password… This password is used by the malware to authenticate to the C2 server.

The threat continues as once the connection is established, the malware contacts the C2 server via the TCP socket and then executes various commands such as “uploading, removing or opening files, executing shell commands, tunneling network traffic, and writing content to files.”

Is It the Chinese Again?

Threat assessors have identified key traits from RedXOR and other malware used by Winnti. ThreatPost lists them as “the PWNLNX backdoor, the XOR.DDOS botnet and the Groundhog botnet . The Winnti threat group (a.k.a. APT41, Barium, Wicked Panda or Wicked Spider) is known for nation-state-backed cyber-espionage activity as well as financial cybercrime.”

All of these threats use open-source kernel rootkits along with other similar functions. What makes researchers confident that the danger comes from China is that “the overall code flow, behavior, and capabilities of RedXOR are very similar to PWNLNX. Both have file uploading and downloading functionalities together with a running shell. The network-tunneling functionality in both families is called ‘PortMap.’”

How to Keep Your Website/Server Safe

During 2020, threat researchers witnessed a severe uptick in Linux-targeted malware and attacks. These incidents don’t appear to be slowing down any time soon. Sophos reported that roughly 70% of organizations use Linux systems for websites or to host data. 

To keep your server and website safe, follow the tips below:

• Keep your server updated with the latest releases, security patches, and apps.

• Be sure your server or hosting company uses strong anti-malware to keep your system safe.

• Install a firewall or configure the one on your server for maximum protection to keep intruders out.

• Always use strong passwords for administration accounts and website logins.

• Be mindful of phishing emails and other fraudulent techniques.

• Never click a link in an email or download attachments.

• Install monitoring software to keep an eye on your website or server 24/7. Most hosting companies do this for you.