Windows Defender Disabled via Registry Modificationedit

Identifies modifications to the Windows Defender registry settings to disable the service or set the service to be started manually.

Rule type: eql

Rule indices:

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

Severity: low

Risk score: 21

Runs every: 5m

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
  • Defense Evasion

Version: 6

Rule authors:

  • Elastic

Rule license: Elastic License v2

Investigation guideedit

## Triage and analysis

### Investigating Windows Defender Disabled via Registry Modification

Microsoft Windows Defender is an antivirus product built into Microsoft Windows, which makes it popular across multiple
environments. Disabling it is a common step in threat actor playbooks.

This rule monitors the registry for configurations that disable Windows Defender or the start of its service.

#### Possible investigation steps

- 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.
- Validate the activity is not related to planned patches, updates, network administrator activity, or legitimate
software installations.
- Identify the user account that performed the action and whether it should perform this kind of action.
- Contact the account owner and confirm whether they are aware of this activity.
- Investigate other alerts associated with the user/host during the past 48 hours.
- Check if this operation is done under change management and approved according to the organization's policy.

### False positive analysis

- This mechanism can be used legitimately. Analysts can dismiss the alert if the administrator is aware of the activity,
the configuration is justified (for example, it is being used to deploy other security solutions or troubleshooting),
and no other suspicious activity has been observed.

### Related rules

- Disabling Windows Defender Security Settings via PowerShell - c8cccb06-faf2-4cd5-886e-2c9636cfcb87
- Microsoft Windows Defender Tampering - fe794edd-487f-4a90-b285-3ee54f2af2d3

### 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.
- Investigate credential exposure on systems compromised or used by the attacker to ensure all compromised accounts are
identified. Reset passwords for these accounts and other potentially compromised credentials, such as email, business
systems, and web services.
- Re-enable Windows Defender and restore the service configurations to automatic start.
- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and
malware components.
- Review the privileges assigned to the user 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 queryedit

registry where event.type in ("creation", "change") and
  (
    (
      registry.path:"HKLM\\SOFTWARE\\Policies\\Microsoft\\Windows Defender\\DisableAntiSpyware" and
      registry.data.strings: ("1", "0x00000001")
   ) or
   (
      registry.path:"HKLM\\System\\*ControlSet*\\Services\\WinDefend\\Start" and
      registry.data.strings in ("3", "4", "0x00000003", "0x00000004")
   )
  )

Framework: MITRE ATT&CKTM