FortiGuard Labs is aware of a new report of a new malware for Linux observed in the wild. Dubbed Shikitega, its attack flow involves multiple modules that are downloaded from a Command and Control (C2) server. Each module has its own purpose and is responsible for downloading and executing the next module. The goal of Shikitega is to deploy XMRig cryptominer, taking control of the compromised Linux machine.
Why is this Significant?
This is significant because Shikitega is a new Linux malware that is designed to take a full control of a compromised machine. It uses variety of attack arsenals: "Shikata Ga Nai" ("it cannot be helped" in Japanese) polymorphic shellcode encoder to evade detection from AV products, exploits for a couple of vulnerabilities for privilege escalation, a Metasploit meterpreter called "Mettle" that enables the attacker to perform a wide range of malicious activities on the infected machine, and XMRig cryptominer for mining Monero.
What is Shikitega Malware?
Shikitega is a malware that is designed to run on Linux machines and consists of small modules.
The Shikitega's infection chain starts with a single dropper containing a payload obfuscated by "Shikata Ga Nai" polymorphic encoder. Once the payload is decrypted and executed, it does not only download the next module from its C2 server but also downloads another dropper module and run them. One new module is a Metasploit meterpreter called "Mettle" that allows the attacker to perform malicious activities on the infected machine such as taking a control of webcams and executing shell commands. The other module is also encoded using "Shikata Ga Nai" and is responsible for downloading another module and executing it with root privileges by exploiting two vulnerabilities (CVE-2021-4034 and CVE-2021-3493). The next module is XMrig, which is a legitimate but oft-abused cryptominer for Monero cryptocurrency.
What Vulnerabilities does Shikitega Exploit?
Shikitega exploits CVE-2021-4034 and CVE-2021-3493 for privilege escalation.
CVE-2021-4034 is a vulnerability in the polkit packages that provide a component for controlling system-wide privileges. This component provides a uniform and organized way for non-privileged processes to communicate with privileged ones. Successful exploitation of the vulnerability an attacker with local network access to gain elevated privileges. The vulnerability has a CVSS score of 7.8 and is included in CISA's Known Exploited Vulnerabilities Catalog.
CVE-2021-3493 is a flaw in the Linux kernel which the overlayfs stacking file system did not properly validate the application of file system capabilities with respect to user namespaces. Successful exploitation of the vulnerability an attacker with local network access to gain elevated privileges. The vulnerability has a CVSS score of 7.4.
Are Patches Available for CVE-2021-4034 and CVE-2021-3493?
Yes, both vulnerabilities have been fixed.
What is the Status of Coverage?
FortiGuard Labs provides the following AV coverage against available samples:
FortiGuard Labs is currently investigating additional coverage for CVE-2021-4034 and CVE-2021-3493. This Threat Signal will be updated when update becomes available.
Shikitega - New stealthy malware targeting Linux (Alien Labs)