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Scheduled Task Execution at Scale via GPO

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Scheduled Task Execution at Scale via GPO

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Detects the modification of Group Policy Object attributes to execute a scheduled task in the objects controlled by the GPO.

Rule type: eql

Rule indices:

winlogbeat-*
logs-system.*
logs-windows.*

Severity: medium

Risk score: 47

Runs every: 5m

Searches indices from: None (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: Privilege Escalation
Tactic: Lateral Movement
Data Source: Active Directory
Resources: Investigation Guide
Use Case: Active Directory Monitoring
Data Source: System

Version: 212

Rule authors:

Elastic

Rule license: Elastic License v2

Investigation guide

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Triage and analysis

Investigating Scheduled Task Execution at Scale via GPO

Group Policy Objects (GPOs) can be used by attackers to execute scheduled tasks at scale to compromise objects controlled by a given GPO. This is done by changing the contents of the <GPOPath>\Machine\Preferences\ScheduledTasks\ScheduledTasks.xml file.

Possible investigation steps

This attack abuses a legitimate mechanism of Active Directory, so it is important to determine whether the activity is legitimate and the administrator is authorized to perform this operation.
Retrieve the contents of the ScheduledTasks.xml file, and check the <Command> and <Arguments> XML tags for any potentially malicious commands or binaries.
Investigate other alerts associated with the user/host during the past 48 hours.
Scope which objects may be compromised by retrieving information about which objects are controlled by the GPO.

False positive analysis

Verify if the execution is allowed and done under change management, and if the execution is legitimate.

Related rules

Group Policy Abuse for Privilege Addition - b9554892-5e0e-424b-83a0-5aef95aa43bf
Startup/Logon Script added to Group Policy Object - 16fac1a1-21ee-4ca6-b720-458e3855d046

Response and remediation

Initiate the incident response process based on the outcome of the triage.
The investigation and containment must be performed in every computer controlled by the GPO, where necessary.
Remove the script from the GPO.
Check if other GPOs have suspicious scheduled tasks attached.
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

The Audit Detailed File Share audit policy must be configured (Success Failure). Steps to implement the logging policy with Advanced Audit Configuration:

Computer Configuration >
Policies >
Windows Settings >
Security Settings >
Advanced Audit Policies Configuration >
Audit Policies >
Object Access >
Audit Detailed File Share (Success,Failure)

The Audit Directory Service Changes audit policy must be configured (Success Failure). Steps to implement the logging policy with Advanced Audit Configuration:

Computer Configuration >
Policies >
Windows Settings >
Security Settings >
Advanced Audit Policies Configuration >
Audit Policies >
DS Access >
Audit Directory Service Changes (Success,Failure)

Rule query

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any where host.os.type == "windows" and event.code in ("5136", "5145") and
(
  (
    winlog.event_data.AttributeLDAPDisplayName : (
      "gPCMachineExtensionNames",
      "gPCUserExtensionNames"
    ) and
    winlog.event_data.AttributeValue : "*CAB54552-DEEA-4691-817E-ED4A4D1AFC72*" and
    winlog.event_data.AttributeValue : "*AADCED64-746C-4633-A97C-D61349046527*"
  ) or
  (
    winlog.event_data.ShareName : "\\\\*\\SYSVOL" and
    winlog.event_data.RelativeTargetName : "*ScheduledTasks.xml" and
    winlog.event_data.AccessList:"*%%4417*"
  )
)

Framework: MITRE ATT&CK^TM

Tactic:
- Name: Privilege Escalation
- ID: TA0004
- Reference URL: https://attack.mitre.org/tactics/TA0004/
Technique:
- Name: Scheduled Task/Job
- ID: T1053
- Reference URL: https://attack.mitre.org/techniques/T1053/
Sub-technique:
- Name: Scheduled Task
- ID: T1053.005
- Reference URL: https://attack.mitre.org/techniques/T1053/005/
Technique:
- Name: Domain or Tenant Policy Modification
- ID: T1484
- Reference URL: https://attack.mitre.org/techniques/T1484/
Sub-technique:
- Name: Group Policy Modification
- ID: T1484.001
- Reference URL: https://attack.mitre.org/techniques/T1484/001/
Tactic:
- Name: Lateral Movement
- ID: TA0008
- Reference URL: https://attack.mitre.org/tactics/TA0008/
Technique:
- Name: Lateral Tool Transfer
- ID: T1570
- Reference URL: https://attack.mitre.org/techniques/T1570/

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