Whitespace Padding in Process Command Line

Identifies process execution events where the command line value contains a long sequence of whitespace characters or multiple occurrences of contiguous whitespace. Attackers may attempt to evade signature-based detections by padding their malicious command with unnecessary whitespace characters. These observations should be investigated for malicious behavior.

Rule type: eql

Rule indices:

winlogbeat-*
logs-endpoint.events.*
logs-windows.*

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:

https://twitter.com/JohnLaTwC/status/1419251082736201737

Tags:

Elastic
Host
Windows
Threat Detection
Defense Evasion

Version: 1

Rule authors:

Elastic

Rule license: Elastic License v2

Investigation guide

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## Triage and analysis

- Analyze the command line of the process in question for evidence of malicious code execution.
- Review the ancestry and child processes spawned by the process in question for indicators of further malicious code execution.

Rule query

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process where event.type in ("start", "process_started") and
  process.command_line regex ".*[ ]{20,}.*" or

  /* this will match on 3 or more separate occurrences of 5+ contiguous whitespace characters */
  process.command_line regex ".*(.*[ ]{5,}[^ ]*){3,}.*"

Framework: MITRE ATT&CK^TM

Tactic:
- Name: Defense Evasion
- ID: TA0005
- Reference URL: https://attack.mitre.org/tactics/TA0005/

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