Adversaries may maintain persistence through executing malicious content triggered using udev rules. Udev is the Linux kernel device manager that dynamically manages device nodes, handles access to pseudo-device files in the /dev directory, and responds to hardware events, such as when external devices like hard drives or keyboards are plugged in or removed. Udev uses rule files with match keys to specify the conditions a hardware event must meet and action keys to define the actions that should follow. Root permissions are required to create, modify, or delete rule files located in /etc/udev/rules.d/, /run/udev/rules.d/, /usr/lib/udev/rules.d/, /usr/local/lib/udev/rules.d/, and /lib/udev/rules.d/. Rule priority is determined by both directory and by the digit prefix in the rule filename.(Citation: Ignacio Udev research 2024)(Citation: Elastic Linux Persistence 2024)
Adversaries may abuse the udev subsystem by adding or modifying rules in udev rule files to execute malicious content. For example, an adversary may configure a rule to execute their binary each time the pseudo-device file, such as /dev/random, is accessed by an application. Although udev is limited to running short tasks and is restricted by systemd-udevd's sandbox (blocking network and filesystem access), attackers may use scripting commands under the action key RUN+= to detach and run the malicious content’s process in the background to bypass these controls.(Citation: Reichert aon sedexp 2024)
| Capability ID | Capability Description | Mapping Type | ATT&CK ID | ATT&CK Name | Notes |
|---|---|---|---|---|---|
| action.malware.variety.Capture app data | Capture data from application or system process | related-to | T1546.017 | Udev Rules | |
| action.malware.variety.Password dumper | Password dumper (extract credential hashes) | related-to | T1546.017 | Udev Rules | |
| action.malware.variety.Spyware/Keylogger | Spyware, keylogger or form-grabber (capture user input or activity) | related-to | T1546.017 | Udev Rules | |
| action.malware.variety.Backdoor | Malware creates a backdoor capability for hacking. Child of 'RAT' when combined with 'Trojan'. Child of 'Backdoor or C2'. | related-to | T1546.017 | Udev Rules |
| Capability ID | Capability Description | Mapping Type | ATT&CK ID | ATT&CK Name | Notes |
|---|---|---|---|---|---|
| google_secops | Google Security Operations | technique_scores | T1546.017 | Udev Rules |
Comments
Google Security Operations is able to trigger alerts based on executed commands that create or modify files where the udev rules are located.
References
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