A new form of Linux malware that is “almost impossible” to detect has been found in a joint research effort by BlackBerry Threat Research & Research team and Intezer security researcher Joakim Kennedy. It has been dubbed Symbiote.
A blog post on the malware was released on Thursday. It has been called Symbiote because of its “parasitic nature.”
Symbiote is different to typical Linux malware because it acts as a shared object (SO) library that is loaded on all running processes via LD_PRELOAD, as opposed to simply attempting to compromise running processes.
The SO library “parasitically” compromises a target machine and the malware provides attackers with rootkit functionality, according to the researchers.
It was found in November 2021 and appears to have been developed to target financial institutions in latin America. The researchers aren’t yet sure whether or not Symbiote is being used in broader or more targeted attacks, if at all.
One of its features is a Berkeley Packet Filter (BPF) hooking, designed to hide malicious traffic on an infected machine. This is used in malware developed by the Equation Group too.
BlackBerry said, “when an administrator starts any packet capture tool on the infected machine, BPF bytecode is injected into the kernel that defines which packets should be captured… In this process, Symbiote adds its bytecode first so it can filter out network traffic that it doesn’t want the packet-capturing software to see.”
The Linux malware has stealth. The malware is pre-loaded before other shared objects, allowing it to hook specific functions to hide its presence. Files associated with Symbiote are concealed and its entire network continually erased.
Symbiote is able to harvest credentials by hooking the libc read function. It allows remote access by hooking Linux Pluggable Authentication Module (PAM) functions.
Domain names associated with Symbiote have impersonated the Federal Police of Brazil and major Brazilian banks.
A sample of the malware was uploaded to VirusTotal and listed under the name certbox64. The uploads might have been for antivirus and detection-testing purposes originally.
