Linux Restricted Shell Breakout via cpulimit Shell Evasion

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Linux Restricted Shell Breakout via cpulimit Shell Evasion

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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.*

Severity: medium

Risk score: 47

Runs every: 5 minutes

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References:

Tags:

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

Version: 1

Added (Elastic Stack release): 8.2.0

Rule authors: Elastic

Rule license: Elastic License v2

Rule query

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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")

Threat mapping

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Framework: MITRE ATT&CKTM