Detect Udev Rules in Microsoft Sentinel
Adversaries may establish persistence by executing malicious content triggered by udev (userspace /dev) rules. Udev is the Linux kernel device manager that handles device events and dynamic file system creation in /dev. Udev rules files (stored at /etc/udev/rules.d/ and /lib/udev/rules.d/) define actions to execute when devices are connected or disconnected, or when other hardware events occur. Adversaries can create malicious udev rules that execute arbitrary commands — potentially as root — when specific device events occur. Since udev runs as root, any RUN directive in a udev rule executes with root privileges, providing both persistence and privilege escalation.
MITRE ATT&CK
- Tactic
- Persistence Privilege Escalation
- Technique
- T1546 Event Triggered Execution
- Sub-technique
- T1546.017 Udev Rules
- Canonical reference
- https://attack.mitre.org/techniques/T1546/017/
KQL Detection Query
DeviceFileEvents
| where Timestamp > ago(24h)
| where (
FolderPath has "/etc/udev/rules.d/"
or FolderPath has "/lib/udev/rules.d/"
or FolderPath has "/usr/lib/udev/rules.d/"
or FolderPath has "/run/udev/rules.d/"
)
| where ActionType in ("FileCreated", "FileModified")
| extend FileName_lc = tolower(FileName)
| extend IsRulesFile = FileName endswith ".rules"
| extend IsEtcRules = FolderPath has "/etc/udev/rules.d/"
| extend SuspiciousWriter = InitiatingProcessFileName !in~ (
"apt", "dpkg", "rpm", "yum", "dnf", "zypper",
"ansible", "puppet", "chef", "salt-minion"
)
| project Timestamp, DeviceName, AccountName, ActionType, FileName, FolderPath,
IsRulesFile, IsEtcRules, SuspiciousWriter,
InitiatingProcessFileName, InitiatingProcessCommandLine
| where IsRulesFile
| sort by Timestamp descDetects udev rules file creation and modification in standard udev rules directories (/etc/udev/rules.d/, /lib/udev/rules.d/, /usr/lib/udev/rules.d/, /run/udev/rules.d/). Monitors for .rules files created or modified by non-package-manager processes. Since udev rules can execute arbitrary commands as root (via RUN directive), any unexpected modification to udev rules directories is a persistence indicator. Files in /etc/udev/rules.d/ are highest priority as they take precedence over system-provided rules.
Data Sources
Required Tables
False Positives & Tuning
- Linux package installations (apt, dpkg, rpm, yum) that install device management rules as part of hardware driver or udev rule packages
- Configuration management tools (Ansible, Puppet, Chef, Salt) that deploy custom udev rules for device configuration as part of system baseline enforcement
- Hardware vendor software that installs udev rules to configure specific hardware devices (e.g., USB security keys, printers, network interfaces)
- System administrators manually creating udev rules to manage device permissions or automate device-triggered workflows
Other platforms for T1546.017
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Create Malicious Udev Rule for USB Device Persistence
Expected signal: File creation event for /etc/udev/rules.d/99-argus-test.rules. Process creation for tee and udevadm. Auditd records for file creation in /etc/udev/rules.d/. When a USB device is inserted, udevd spawns bash to execute the RUN directive — child process of udevd.
- Test 2Create Udev Rule Triggered by Network Interface
Expected signal: File creation event for 99-argus-net-test.rules in /etc/udev/rules.d/. The rule fires when a network interface is added — logger is spawned by udevd as a child process, creating a syslog entry. Systemd journal shows udevd running the RUN directive.
- Test 3Enumerate All Custom Udev Rules
Expected signal: Process creation for grep, ls with udev directory arguments. Read-only — no modifications. The output reveals all custom rules and their RUN directives.
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