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 New Linux Malware Syslogk has a Clever Approach of Staying Undetected

Avast claims that using Syslogk and Rebooke on a bogus SMTP server gives an attacker a strong toolkit.

 

Syslogk, a newfound clever form of Linux malware, installs a backdoor that remains hidden on the target device until its controller sends so-called 'magic packets' from anywhere on the internet. It is mostly based on Adore-Ng, a Chinese open-source kernel rootkit for Linux. 

Adore-Ng which has been around since 2004, is a free open-source rootkit, that gives an attacker complete control over an infected system. Syslogk can force-load its packages into the Linux kernel (versions 3. x are supported), hide folders or spoof files and network traffic, and ultimately load a backdoor named 'Rekoobe.' 

How does the malware work?

Syslogk was originally discovered in early 2022, with the sample constructed for a specific kernel version – meaning it could be loaded without being forced – and the payload named PgSD93ql, which disguised it as a PostgreSQL file. 

"Rekoobe is a piece of code that has been placed in genuine servers," according to Avast security researchers. "In this case, it's embedded in a phony SMTP server that, when given a specially designed command, spawns a shell." 

The rootkit was created to hide harmful files, malicious software, and its malicious payload from showing on the list of operating services, to deliver the malicious payload when it received a specially constructed TCP packet, and to halt the payload if the attacker directed it to. 

Rekoobe appears to be a harmless SMTP server, but it is built on an open-source project called Tiny SHell, so it contains a backdoor command for generating a shell that allows it to run arbitrary instructions for data mining. Despite the restricted support for Linux kernel versions, Avast claims that using Syslogk and Rebooke on a bogus SMTP server gives an attacker a strong toolkit. 

The Syslogk rootkit is yet one piece of highly evasive malware for Linux systems, joining the likes of Symbiote and BPFDoor, which both exploit the BPF system to monitor and dynamically change network traffic. Ransomware campaigns, crypto attacks, and other data theft illicit behavior are increasingly being launched against Linux systems and cloud infrastructure making it a vulnerable target. 
 
As in the case of Syslogk, the initiative is in its early stages of development, so it's unclear whether it'll become a wide-scale threat. However, given its secrecy, it will almost certainly continue to release new and improved versions.
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