Cybersecurity researchers have uncovered a brand new stealthy piece of Linux malware that leverages an unconventional approach to realize persistence on contaminated methods and conceal bank card skimmer code.
The malware, attributed to a financially motivated menace actor, has been codenamed sedexp by Aon’s Stroz Friedberg incident response providers staff.
“This superior menace, lively since 2022, hides in plain sight whereas offering attackers with reverse shell capabilities and superior concealment techniques,” researchers Zachary Reichert, Daniel Stein, and Joshua Pivirotto stated.
It is not stunning that malicious actors are always improvising and refining their tradecraft, and have turned to novel methods to evade detection.
What makes sedexp noteworthy is its use of udev guidelines to keep up persistence. Udev, substitute for the Machine File System, gives a mechanism to determine gadgets 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 not less than as soon as key-value pair, making it doable to match gadgets by identify and set off sure actions when varied system occasions are detected (e.g., set off an computerized backup when an exterior drive is hooked up).
“An identical rule could specify the identify 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 identify is used to create the system node.”
The udev rule for sedexp — ACTION==”add”, ENV{MAJOR}==”1″, ENV{MINOR}==”8″, RUN+=”asedexpb run:+” — is about up such that the malware is run every time /dev/random (corresponds to system minor quantity 8) is loaded, which usually happens upon each reboot.
Put in another way, 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 stated within the cases it investigated, the potential has been put to make use of to cover net shells, altered Apache configuration information, and the udev rule itself.
“The malware was used to cover bank card scraping code on an internet server, indicating a concentrate on monetary achieve,” the researchers stated. “The invention of sedexp demonstrates the evolving sophistication of financially motivated menace actors past ransomware.”