Scheduled Task/Job: Таймеры systemd
Other sub-techniques of Scheduled Task/Job (7)
Adversaries may abuse systemd timers to perform task scheduling for initial or recurring execution of malicious code. Systemd timers are unit files with file extension .timer
that control services. Timers can be set to run on a calendar event or after a time span relative to a starting point. They can be used as an alternative to Cron in Linux environments.(Citation: archlinux Systemd Timers Aug 2020) Systemd timers may be activated remotely via the systemctl
command line utility, which operates over SSH.(Citation: Systemd Remote Control)
Each .timer
file must have a corresponding .service
file with the same name, e.g., example.timer
and example.service
. .service
files are Systemd Service unit files that are managed by the systemd system and service manager.(Citation: Linux man-pages: systemd January 2014) Privileged timers are written to /etc/systemd/system/
and /usr/lib/systemd/system
while user level are written to ~/.config/systemd/user/
.
An adversary may use systemd timers to execute malicious code at system startup or on a scheduled basis for persistence.(Citation: Arch Linux Package Systemd Compromise BleepingComputer 10JUL2018)(Citation: gist Arch package compromise 10JUL2018)(Citation: acroread package compromised Arch Linux Mail 8JUL2018) Timers installed using privileged paths may be used to maintain root level persistence. Adversaries may also install user level timers to achieve user level persistence.(Citation: Falcon Sandbox smp: 28553b3a9d)
Контрмеры |
|
Контрмера | Описание |
---|---|
Restrict File and Directory Permissions |
Restrict access by setting directory and file permissions that are not specific to users or privileged accounts. |
User Account Management |
Manage the creation, modification, use, and permissions associated to user accounts. |
Privileged Account Management |
Manage the creation, modification, use, and permissions associated to privileged accounts, including SYSTEM and root. |
Обнаружение
Systemd timer unit files may be detected by auditing file creation and modification events within the /etc/systemd/system
, /usr/lib/systemd/system/
, and ~/.config/systemd/user/
directories, as well as associated symbolic links. Suspicious processes or scripts spawned in this manner will have a parent process of ‘systemd’, a parent process ID of 1, and will usually execute as the ‘root’ user.
Suspicious systemd timers can also be identified by comparing results against a trusted system baseline. Malicious systemd timers may be detected by using the systemctl utility to examine system wide timers: systemctl list-timers –all
. Analyze the contents of corresponding .service
files present on the file system and ensure that they refer to legitimate, expected executables.
Audit the execution and command-line arguments of the 'systemd-run' utility as it may be used to create timers.(Citation: archlinux Systemd Timers Aug 2020)
Ссылки
- Linux man-pages. (2014, January). systemd(1) - Linux manual page. Retrieved April 23, 2019.
- Hybrid Analysis. (2018, July 11). HybridAnalsysis of sample 28553b3a9d2ad4361d33d29ac4bf771d008e0073cec01b5561c6348a608f8dd7. Retrieved September 8, 2023.
- Eli Schwartz. (2018, June 8). acroread package compromised. Retrieved April 23, 2019.
- Catalin Cimpanu. (2018, July 10). Malware Found in Arch Linux AUR Package Repository. Retrieved April 23, 2019.
- Catalin Cimpanu. (2018, July 10). ~x file downloaded in public Arch package compromise. Retrieved April 23, 2019.
- archlinux. (2020, August 11). systemd/Timers. Retrieved October 12, 2020.
- Aaron Kili. (2018, January 16). How to Control Systemd Services on Remote Linux Server. Retrieved July 26, 2021.
Связанные риски
Риск | Связи | |
---|---|---|
Закрепление злоумышленника в ОС
из-за
создания или изменение задачи таймера Systemd
в ОС Linux
Повышение привилегий
НСД
|
1
|
|
Повышение привилегий в ОС
из-за
создания или изменение задачи таймера Systemd
в ОС Linux
Повышение привилегий
Целостность
|
1
|
Каталоги
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