ESET Discovers New Linux Malware
WolfsBane is an all-in-one malware that has hit the Linux operating system and includes a dropper, a launcher, and a backdoor.
WolfsBane, a Chinese malware, has been discovered by ESET and is being used by a group known as Gelsemium. This malware is listed as an all-in-one because it contains everything necessary to do what it needs to do, including a dropper (named cron), which “drops” the launcher disguised as a KDE desktop component. WolfsBane then (if needed) disables SELinux, creates required system service files, and/or modifies a configuration for persistence. The malware also includes the Hider rootkit, which is capable of hooking into functions like open, stat, readdir, and access. The reason why this is labeled an all-in-one is because it doesn't depend on the work of others to succeed; everything is included. WolfsBane's key feature is the ability to grant control over a compromised system to those deploying it.
ESET isn't sure how the attackers are deploying WolfsBane, but it does know that Gelsemium (active since 2014) exploited a previously unknown web application vulnerability. As of now, the primary targets of WolfsBane are in East Asia and the Middle East.
This also comes at the same time that a backdoor (named FireWood) has been discovered within a file named usbdev.ko, which is a kernel driver module that works as a rootkit to hide processes. FireWood then uses a configuration file, kdeinit, that is encrypted with a single-byte key and renames its process based on the value within the configuration file.
ESET has said that although they "lack concrete evidence regarding the initial access vector, the presence of multiple webshells…and the tactics, techniques, and procedures (TTPs) used by the Gelsemium APT group in recent years, we conclude with medium confidence that the attackers exploited an unknown web application vulnerability to gain server access."
