Linux Restricted Shell Breakout via the expect command

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Linux Restricted Shell Breakout via the expect command

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Identifies Linux binary expect command abuse to break out from restricted environments by spawning an interactive system shell. The expect utility allows us to automate control of interactive applications such as Telnet, FTP, SSH and others. The activity of spawning shell is not a standard use of this binary for a user or system administrator and could potentially indicate 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 == "expect" and process.parent.args
== "-c" and process.parent.args in ("spawn /bin/sh;interact", "spawn
/bin/bash;interact", "spawn /bin/dash;interact", "spawn sh;interact",
"spawn bash;interact", "spawn dash;interact")

Threat mapping

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Framework: MITRE ATT&CKTM