Creation of a Hidden Local User Account

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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: 5 minutes

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References:

Tags:

  • Elastic
  • Host
  • Windows
  • Threat Detection
  • Persistence

Version: 4 (version history)

Added (Elastic Stack release): 7.12.0

Last modified (Elastic Stack release): 8.3.0

Rule authors: Elastic

Rule license: Elastic License v2

Investigation guide

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## Triage and analysis

### Investigating Creation of a Hidden Local User Account

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.

#### Possible investigation steps

- Identify the user account that performed the action and whether it should perform this kind of action.
- Investigate the process execution chain (parent process tree) for unknown processes. Examine their executable files for
prevalence, whether they are located in expected locations, and if they are signed with valid digital signatures.
- Investigate other alerts associated with the user/host during the past 48 hours.

### False positive analysis

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

### Response and remediation

- Initiate the incident response process based on the outcome of the triage.
- Isolate the involved hosts to prevent further post-compromise behavior.
- Delete the hidden account.
- Review the privileges assigned to the involved users to ensure that the least privilege principle is being followed.
- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
- Using the incident response data, update logging and audit policies to improve the mean time to detect (MTTD) and the
mean time to respond (MTTR).

## 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.

Rule query

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

Threat mapping

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Framework: MITRE ATT&CKTM

Rule version history

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Version 4 (8.3.0 release)
  • Formatting only
Version 3 (8.2.0 release)
  • Formatting only
Version 2 (7.16.0 release)
  • Formatting only