Detect RC Scripts in Elastic Security
Adversaries may establish persistence by modifying RC scripts, which are executed during a Unix-like system's startup. These files allow system administrators to map and start custom services at startup for different run levels. RC scripts require root privileges to modify. Adversaries may add malicious binary paths or shell commands to rc.local, rc.common, and other RC scripts. Upon reboot, the system executes the script's contents as root, resulting in persistence. This technique is especially effective on ESXi hypervisors, IoT devices, and embedded systems. Notable threat actors using this technique include HiddenWasp, UNC3886, APT29, Velvet Ant, Green Lambert, Cyclops Blink, and iKitten.
MITRE ATT&CK
- Tactic
- Persistence Privilege Escalation
- Sub-technique
- T1037.004 RC Scripts
- Canonical reference
- https://attack.mitre.org/techniques/T1037/004/
Elastic Detection Query
any where
(
(
event.category == "file" and
event.type in ("creation", "change") and
(
file.path like~ "/etc/rc.local" or
file.path like~ "/etc/rc.common" or
file.path like~ "/etc/rc.d/*" or
file.path like~ "/etc/init.d/*" or
file.path like~ "/etc/rc.local.d/*" or
file.path like~ "/etc/rc0.d/*" or
file.path like~ "/etc/rc1.d/*" or
file.path like~ "/etc/rc2.d/*" or
file.path like~ "/etc/rc3.d/*" or
file.path like~ "/etc/rc4.d/*" or
file.path like~ "/etc/rc5.d/*" or
file.path like~ "/etc/rc6.d/*" or
file.name in ("rc.local", "rc.common", "local.sh")
)
) or
(
event.category == "process" and
event.type == "start" and
process.name in ("bash", "sh", "dash", "zsh", "python", "python3", "perl", "ruby", "curl", "wget", "nc", "netcat", "ncat", "tee", "dd") and
(
process.args like~ "*/etc/rc.local*" or
process.args like~ "*/etc/rc.common*" or
process.args like~ "*/etc/rc.d/*" or
process.args like~ "*/etc/init.d/*" or
process.args like~ "*/etc/rc.local.d/*"
) and
(
process.args : "echo" or process.args : "tee" or process.args : "cat" or
process.args : "sed" or process.args : "awk" or process.args : ">>"
)
)
)Detects RC script persistence via file creation/modification events in /etc/rc.local, /etc/rc.d/, and related directories, as well as process-based writes using shells, interpreters, or download tools targeting these paths.
Data Sources
Required Tables
False Positives & Tuning
- System administrators legitimately editing /etc/rc.local or /etc/init.d/ scripts during maintenance windows or software deployments
- Package managers (apt, yum, dpkg) creating or modifying init.d service scripts as part of software installation
- Configuration management tools (Ansible, Puppet, Chef, SaltStack) writing startup scripts as part of automated provisioning workflows
Other platforms for T1037.004
Testing Methodology
Validate this detection against 4 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 1Add Malicious Entry to /etc/rc.local
Expected signal: Auditd: syscall records for open()/write() on /etc/rc.local by the test user (root). Sysmon for Linux Event ID 11 (FileCreate) if deployed. Shell history: echo commands with /etc/rc.local in root's .bash_history. File modification timestamp change on /etc/rc.local visible via 'stat /etc/rc.local'.
- Test 2Create Persistent Backdoor via ESXi local.sh
Expected signal: File creation/modification events for /etc/rc.local.d/local.sh. Process creation events for chmod, echo, cat commands with /etc/rc.local.d/ in command line. On actual ESXi: /var/log/shell.log entries for each command executed in the ESXi shell.
- Test 3Add init.d Script for Persistence
Expected signal: File creation event for /etc/init.d/argus-test-service. Process creation events for cat, chmod commands. Shell history entries. If auditd is configured with watch on /etc/init.d/: syscall records for openat/write/chmod syscalls.
- Test 4Write Binary Path from Temp Directory to rc.local
Expected signal: File creation events for /tmp/.argus_test_binary (hidden file in /tmp is suspicious). File modification event for /etc/rc.local. Process creation events for echo, chmod, cat commands. Auditd syscall records for both /tmp/ and /etc/rc.local file writes. The combination of hidden file in /tmp plus /etc/rc.local modification is a high-fidelity indicator.
References (11)
- https://attack.mitre.org/techniques/T1037/004/
- https://www.intezer.com/blog-hiddenwasp-malware-targeting-linux-systems/
- https://www.intezer.com/blog/research/kaiji-new-chinese-linux-malware-turning-to-golang/
- https://blogs.juniper.net/en-us/threat-research/a-custom-python-backdoor-for-vmware-esxi-servers
- https://iranthreats.github.io/resources/attribution-flying-rocket-kitten/
- http://manpages.ubuntu.com/manpages/bionic/man8/systemd-rc-local-generator.8.html
- https://developer.apple.com/library/archive/documentation/MacOSX/Conceptual/BPSystemStartup/Chapters/CreatingLaunchdJobs.html
- https://www.virusbulletin.com/uploads/pdf/conference/vb2014/VB2014-Wardle.pdf
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1037.004/T1037.004.md
- https://www.sygnia.co/blog/velvet-ant-f5-big-ip-zero-day-cve-2023-46747
- https://cloud.google.com/blog/topics/threat-intelligence/esxi-hypervisors-malware-persistence
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