Linux Restricted Shell Breakout via env Shell Evasion

Identifies Linux binary env abuse to break out from restricted environments by spawning an interactive system shell. The env utility is a shell command for Unix-like operating systems and is used to print a list of environment variables. The activity of spawning a shell is not a standard use of this binary for 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/env/

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 : "env" and process.args_count == 2 and process.args : ("/bin/sh", "/bin/bash", "sh", "bash")
		

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/