Linux Restricted Shell Breakout via flock Shell evasionedit

Identifies Linux binary flock abuse to break out from restricted environments by spawning an interactive system shell. The flock utility allows users to manage advisory file locks in shell scripts or on the command line. The activity of spawning 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:


Severity: medium

Risk score: 47

Runs every: 5m

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

Maximum alerts per execution: 100



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

Version: 2

Rule authors:

  • Elastic

Rule license: Elastic License v2

Rule queryedit

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