Linux Restricted Shell Breakout via cpulimit Shell Evasion

Identifies Linux binary cpulimit abuse to break out from restricted environments by spawning an interactive system shell. The cpulimit utility is used to restrict the CPU usage of a process in cases of CPU or system load exceeding the defined threshold and the activity of spawning a shell is not a standard use of this binary by a user or system administrator. This can potentially indicate a malicious actor attempting to improve the capabilities or stability of their access.

Rule type: eql
Rule indices:

• logs-endpoint.events.*

Rule Severity: medium
Risk Score: 47
Runs every:
Searches indices from: now-9m
Maximum alerts per execution: 100
References:

• https://gtfobins.github.io/gtfobins/cpulimit/

Tags:

• Elastic
• Host
• Linux
• Threat Detection
• Execution
• GTFOBins

Version: 100
Rule authors:

• Elastic

Rule license: Elastic License v2

process where event.type == "start" and process.name in ("bash", "sh", "dash") and
  process.parent.name == "cpulimit" and process.parent.args == "-f" and
  process.parent.args in ("/bin/sh", "/bin/bash", "/bin/dash", "sh", "bash", "dash")
		

Framework: MITRE ATT&CK

• Tactic:

  • Name: Execution
  • Id: TA0002
  • Reference URL: https://attack.mitre.org/tactics/TA0002/

• Technique:

  • Name: Command and Scripting Interpreter
  • Id: T1059
  • Reference URL: https://attack.mitre.org/techniques/T1059/

• Sub Technique:

  • Name: Unix Shell
  • Id: T1059.004
  • Reference URL: https://attack.mitre.org/techniques/T1059/004/