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:

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:

Version: 9

Rule authors:

Rule license: Elastic License v2

## Triage and analysis

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

## Config

If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2, events will not define `event.ingested` and default fallback for EQL rules was not added until 8.2, so you will need to add a custom pipeline to populate `event.ingested` to @timestamp for this rule to work.

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 3+ contiguous whitespace characters */
  process.command_line regex "([^ ]+[ ]{3,}[^ ]*){3,}.*"