Cybersecurity researchers have uncovered a brand new stealthy piece of Linux malware that leverages an unconventional approach to realize persistence on contaminated techniques and conceal bank card skimmer code.
The malware, attributed to a financially motivated risk actor, has been codenamed sedexp by Aon’s Stroz Friedberg incident response companies group.
“This superior risk, energetic since 2022, hides in plain sight whereas offering attackers with reverse shell capabilities and superior concealment ways,” researchers Zachary Reichert, Daniel Stein, and Joshua Pivirotto mentioned.
It is not shocking that malicious actors are continuously improvising and refining their tradecraft, and have turned to novel strategies to evade detection.
What makes sedexp noteworthy is its use of udev guidelines to take care of persistence. Udev, alternative for the Machine File System, affords a mechanism to establish units based mostly on their properties and configure guidelines to reply when there’s a change within the system state, i.e., a tool is plugged in or eliminated.
Every line within the udev guidelines file has a minimum of as soon as key-value pair, making it potential to match units by title and set off sure actions when numerous system occasions are detected (e.g., set off an automated backup when an exterior drive is hooked up).
“An identical rule might specify the title of the system node, add symbolic hyperlinks pointing to the node, or run a specified program as a part of the occasion dealing with,” SUSE Linux notes in its documentation. “If no matching rule is discovered, the default system node title is used to create the system node.”
The udev rule for sedexp — ACTION==”add”, ENV{MAJOR}==”1″, ENV{MINOR}==”8″, RUN+=”asedexpb run:+” — is ready up such that the malware is run at any time when /dev/random (corresponds to system minor quantity 8) is loaded, which usually happens upon each reboot.
Put otherwise, this system specified within the RUN parameter is executed each time after a system restart.
The malware comes with capabilities to launch a reverse shell to facilitate distant entry to the compromised host, in addition to modify reminiscence to hide any file containing the string “sedexp” from instructions like ls or discover.
Stroz Friedberg mentioned within the cases it investigated, the aptitude has been put to make use of to cover net shells, altered Apache configuration recordsdata, and the udev rule itself.
“The malware was used to cover bank card scraping code on an internet server, indicating a give attention to monetary achieve,” the researchers mentioned. “The invention of sedexp demonstrates the evolving sophistication of financially motivated risk actors past ransomware.”