Linux Restricted Shell Breakout via cpulimit Shell Evasion
Elastic Stack Serverless Security
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: 5m
Searches indices from: now-9m (https://www.elastic.co/guide/en/elasticsearch/reference/current/common-options.html#date-math[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
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")
Framework: MITRE ATT&CKTM
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/