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Linux Restricted Shell Breakout via c89/c99 Shell evasion

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Linux Restricted Shell Breakout via c89/c99 Shell evasion

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Identifies Linux binary c89/c99 abuse to break out from restricted environments by spawning an interactive system shell.The c89/c99 utility is an interface to the standard C compilation system 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.*

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

References:

Tags:

Elastic
Host
Linux
Threat Detection
Execution
GTFOBins

Version: 1

Rule authors:

Elastic

Rule license: Elastic License v2

Rule query

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process where event.type == "start" and process.name in ("sh", "dash", "bash") and
  process.parent.name in ("c89","c99") and process.parent.args == "-wrapper" and
  process.parent.args in ("sh,-s", "bash,-s", "dash,-s", "/bin/sh,-s", "/bin/bash,-s", "/bin/dash,-s")

Framework: MITRE ATT&CK^TM

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/

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