According to the researchers from the Elastic Security Lab, a new rootkit called PUMAKIT can perform various advanced evasion mechanisms. When Elastic Security researchers discovered PUMAKIT while routinely hunting for threats on VirusTotal, they described it as PUMAKIT. Many stages are involved in deploying this multi-stage malware, including a dropper, two memory-resident executables, an LKM rootkit module, and a shared object rootkit, all of which are used in the userland. 

To manipulate core system behaviours, the rootkit component can hook into 18 different syscalls and several kernel functions using an internal Linux function tracer (ftrace), which enables it to control the behaviour of core system components. The rootkit is an advanced persistent threat (APT) that tends to target critical organizations with specific programs designed to establish persistence within compromised systems.

The rootkit is often used by APT groups in their attempts to target critical organizations with specific programs. As a result of the discovery of this Linux rootkit malware called Pumakit, it can evade detection and compromise systems through advanced stealth and privilege escalation techniques. Several components make up this sophisticated malware, including a dropper, a memory-resident executable, kernel module rootkits, and userland rootkits. 

The Pumakit malware family was discovered by Elastic Security in a suspicious binary 'cron' uploaded to VirusTotal on September 4, 2024. The details surrounding its identity and target remain vague. There are a variety of rootkits like this that are commonly used by advanced threat actors to undermine critical infrastructure, steal money, disrupt operations, and infiltrate enterprise systems to conduct espionage. As a sophisticated piece of malware, PUMAKIT was discovered via routine threat detection on VirusTotal as part of routine threat hunting. 

Its binary contains strings embedded by the developer that can be easily identified and accessed by developers. There is an internal structure to the malware that is based on a multi-stage architecture, which comprises a dropper component named "cron", two memory-resident executables called TGT and WPN, an LKM rootkit called Pumba and a shared object rootkit called Kitsune that is bundled in with the malware. This payload allows for loading the LKM rootkit ('puma.ko') into the kernel as well as the userland rootkit ('Kitsune SO') to intercept system calls via the userland.  

A kernel function, such as "prepare_creds" and "commit_creds," can also be used to alter core system behaviour and achieve its objectives. It includes the use of the internal Linux function tracer (trace) to hook into as many as 18 different system calls and various kernel functions, such as "prepare_creds." and "commit_creds." In addition, Elastic noted that every step of the infection chain is designed to conceal the malware's presence, leveraging memory-resident files, and doing specific checks before unleashing the rootkit, which will make it difficult for the user to detect it before it is launched. 

As of right now, the company has not linked PUMAKIT to any known threat actor or group and believes that the software most likely originated from unknown sources. As you may know, PUMAKIT is a sophisticated and stealthy threat, which utilizes advanced techniques like syscall hooks, memory-resident execution, and unique methods for escalating privileges. According to the researchers, it is a multi-architectural malware that demonstrates the increasing sophistication of malware aimed at Linux. For IForthe LKM rootkit to be able to manipulate the behaviour of a system, it must use the syscall table, as well as kallsyms_lookup_name() to find symbol names. 

Rootkits targeting kernel versions 5.7 and above tend to use probes, which means they are designed for older kernels which makes them more difficult to detect than modern rootkits. There has been a debate within the kernel development team about the unsporting of the kallsyms_lookup_name() code to prevent unauthorized or malicious modules from misusing it. As part of this tactic, modules are often added with fake MODULE_LICENSE("GPL") declarations that circumvent license checks, thereby allowing them to access non-exported kernel functions, which is not permitted under the GPL.

A Linux rootkit known as PUMAKIT, or Pumakkit for short, has been discovered that underscores the sophistication with which Linux systems are being targeted by targeted threats. This malware is one of the most dangerous adversaries because it can evade detection and execute advanced attacks. In any case, proactive measures can reduce the harm caused by these threats by recommending regular updates and by increasing monitoring capabilities, among other measures. 

To defend against attacks like PUMAKIT being carried out by hackers like Kumak, it is crucial to remain informed and vigilant in the face of evolving cybersecurity threats. Users must take every precaution to ensure that their Linux systems are protected from this and other advanced malware threats.