Linux Restricted Shell Breakout via busybox Shell Evasion

Identifies Linux binary busybox abuse to break out from restricted environments by spawning an interactive system shell.The busybox is software utility suite that provides several Unix utilities in a single executable file and the activity of spawing a shell is not a standard use of this binary by a user or system administrator. It indicates a potentially 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/busybox/

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 == "busybox" and process.args_count == 2 and process.args in ("/bin/sh", "/bin/ash", "sh", "ash")
		

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/