Creation of a Hidden Local User Account

Elastic Stack Serverless Security

Identifies the creation of a hidden local user account by appending the dollar sign to the account name. This is sometimes done by attackers to increase access to a system and avoid appearing in the results of accounts listing using the net users command.

Rule type: eql

Rule indices:

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

Severity: high

Risk score: 73

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:

• https://web.archive.org/web/20230329153858/https://blog.menasec.net/2019/02/threat-hunting-6-hiding-in-plain-sights_8.html
• https://github.com/CyberMonitor/APT_CyberCriminal_Campagin_Collections/tree/master/2020/2020.12.15.Lazarus_Campaign

Tags:

• Elastic
• Host
• Windows
• Threat Detection
• Persistence

Version: 3

Rule authors:

• Elastic

Rule license: Elastic License v2

Attackers can create accounts ending with a $ symbol to make the account hidden to user enumeration utilities and
bypass detections that identify computer accounts by this pattern to apply filters.

This rule uses registry events to identify the creation of local hidden accounts.

• Identify the user account which performed the action and whether it should perform this kind of action.
• Investigate the script execution chain (parent process tree).
• Investigate other alerts related to the user/host in the last 48 hours.

• This activity is unlikely to happen legitimately. Benign true positive (B-TPs) can be added as exceptions if necessary.

• Initiate the incident response process based on the outcome of the triage.
• Quarantine the involved host to prevent further post-compromise behavior.
• Delete the hidden account.
• Review the privileges of the involved accounts.

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.

registry where registry.path : "HKLM\\SAM\\SAM\\Domains\\Account\\Users\\Names\\*$\\"

Framework: MITRE ATT&CKTM

• Tactic:

  • Name: Persistence
  • ID: TA0003
  • Reference URL: https://attack.mitre.org/tactics/TA0003/

• Technique:

  • Name: Create Account
  • ID: T1136
  • Reference URL: https://attack.mitre.org/techniques/T1136/

• Sub-technique:

  • Name: Local Account
  • ID: T1136.001
  • Reference URL: https://attack.mitre.org/techniques/T1136/001/