Creation of Hidden Files and Directories via CommandLine

Users can mark specific files as hidden simply by putting a "." as the first character in the file or folder name. Adversaries can use this to their advantage to hide files and folders on the system for persistence and defense evasion. This rule looks for hidden files or folders in common writable directories.

Rule type: eql

Rule indices:

auditbeat-*
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: 33

References: None

Tags:

Elastic
Host
Linux
Threat Detection
Defense Evasion

Version: 11

Rule authors:

Elastic

Rule license: Elastic License v2

Investigation guide

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## Setup

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.

Rule query

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process where event.type in ("start", "process_started") and
  process.working_directory in ("/tmp", "/var/tmp", "/dev/shm") and
  process.args regex~ """\.[a-z0-9_\-][a-z0-9_\-\.]{1,254}""" and
  not process.name in ("ls", "find", "grep")

Framework: MITRE ATT&CK^TM

Tactic:
- Name: Defense Evasion
- ID: TA0005
- Reference URL: https://attack.mitre.org/tactics/TA0005/
Technique:
- Name: Hide Artifacts
- ID: T1564
- Reference URL: https://attack.mitre.org/techniques/T1564/
Sub-technique:
- Name: Hidden Files and Directories
- ID: T1564.001
- Reference URL: https://attack.mitre.org/techniques/T1564/001/
Tactic:
- Name: Persistence
- ID: TA0003
- Reference URL: https://attack.mitre.org/tactics/TA0003/

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