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Microsoft Windows Defender Tampering

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Microsoft Windows Defender Tampering

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Identifies when one or more features on Microsoft Defender are disabled. Adversaries may disable or tamper with Microsoft Defender features to evade detection and conceal malicious behavior.

Rule type: eql

Rule indices:

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

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:

  • Domain: Endpoint
  • OS: Windows
  • Use Case: Threat Detection
  • Tactic: Defense Evasion
  • Resources: Investigation Guide
  • Data Source: Elastic Defend
  • Data Source: Sysmon

Version: 110

Rule authors:

  • Austin Songer

Rule license: Elastic License v2

Investigation guide

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Triage and analysis

Investigating Microsoft Windows Defender Tampering

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 modifications that disable Windows Defender features.

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.
  • Examine which features have been disabled, and 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

  • Windows Defender Disabled via Registry Modification - 2ffa1f1e-b6db-47fa-994b-1512743847eb
  • Disabling Windows Defender Security Settings via PowerShell - c8cccb06-faf2-4cd5-886e-2c9636cfcb87

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.
  • Take actions to restore the appropriate Windows Defender antivirus configurations.
  • 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).

Setup

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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 version 8.2. Hence for this rule to work effectively, users will need to add a custom ingest pipeline to populate event.ingested to @timestamp. For more details on adding a custom ingest pipeline refer - https://www.elastic.co/guide/en/fleet/current/data-streams-pipeline-tutorial.html

Rule query

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registry where host.os.type == "windows" and event.type in ("creation", "change") and
  (registry.path : "HKLM\\SOFTWARE\\Policies\\Microsoft\\Windows Defender\\PUAProtection" and
  registry.data.strings : ("0", "0x00000000")) or
  (registry.path : "HKLM\\SOFTWARE\\Policies\\Microsoft\\Windows Defender Security Center\\App and Browser protection\\DisallowExploitProtectionOverride" and
  registry.data.strings : ("0", "0x00000000")) or
  (registry.path : "HKLM\\SOFTWARE\\Policies\\Microsoft\\Windows Defender\\DisableAntiSpyware" and
  registry.data.strings : ("1", "0x00000001")) or
  (registry.path : "HKLM\\SOFTWARE\\Policies\\Microsoft\\Windows Defender\\Features\\TamperProtection" and
  registry.data.strings : ("0", "0x00000000")) or
  (registry.path : "HKLM\\SOFTWARE\\Policies\\Microsoft\\Windows Defender\\Real-Time Protection\\DisableRealtimeMonitoring" and
  registry.data.strings : ("1", "0x00000001")) or
  (registry.path : "HKLM\\SOFTWARE\\Policies\\Microsoft\\Windows Defender\\Real-Time Protection\\DisableIntrusionPreventionSystem" and
  registry.data.strings : ("1", "0x00000001")) or
  (registry.path : "HKLM\\SOFTWARE\\Policies\\Microsoft\\Windows Defender\\Real-Time Protection\\DisableScriptScanning" and
  registry.data.strings : ("1", "0x00000001")) or
  (registry.path : "HKLM\\SOFTWARE\\Policies\\Microsoft\\Windows Defender\\Windows Defender Exploit Guard\\Controlled Folder Access\\EnableControlledFolderAccess" and
  registry.data.strings : ("0", "0x00000000")) or
  (registry.path : "HKLM\\SOFTWARE\\Policies\\Microsoft\\Windows Defender\\Real-Time Protection\\DisableIOAVProtection" and
  registry.data.strings : ("1", "0x00000001")) or
  (registry.path : "HKLM\\SOFTWARE\\Policies\\Microsoft\\Windows Defender\\Reporting\\DisableEnhancedNotifications" and
  registry.data.strings : ("1", "0x00000001")) or
  (registry.path : "HKLM\\SOFTWARE\\Policies\\Microsoft\\Windows Defender\\SpyNet\\DisableBlockAtFirstSeen" and
  registry.data.strings : ("1", "0x00000001")) or
  (registry.path : "HKLM\\SOFTWARE\\Policies\\Microsoft\\Windows Defender\\SpyNet\\SpynetReporting" and
  registry.data.strings : ("0", "0x00000000")) or
  (registry.path : "HKLM\\SOFTWARE\\Policies\\Microsoft\\Windows Defender\\SpyNet\\SubmitSamplesConsent" and
  registry.data.strings : ("0", "0x00000000")) or
  (registry.path : "HKLM\\SOFTWARE\\Policies\\Microsoft\\Windows Defender\\Real-Time Protection\\DisableBehaviorMonitoring" and
  registry.data.strings : ("1", "0x00000001"))

Framework: MITRE ATT&CKTM

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