Scheduled Task Execution at Scale via GPO

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:

• logs-system.security*
• logs-windows.forwarded*
• winlogbeat-*

Rule Severity: medium
Risk Score: 47
Runs every:
Searches indices from: ``
Maximum alerts per execution: ?
References:

• https://github.com/atc-project/atc-data/blob/master/docs/Logging_Policies/LP_0025_windows_audit_directory_service_changes.md
• https://github.com/atc-project/atc-data/blob/f2bbb51ecf68e2c9f488e3c70dcdd3df51d2a46b/docs/Logging_Policies/LP_0029_windows_audit_detailed_file_share.md
• https://labs.f-secure.com/tools/sharpgpoabuse
• https://twitter.com/menasec1/status/1106899890377052160
• https://github.com/SigmaHQ/sigma/blob/master/rules/windows/builtin/security/win_gpo_scheduledtasks.yml

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: Windows Security Event Logs

Version: ?
Rule authors:

• Elastic

Rule license: Elastic License v2

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)

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.

• 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.

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

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

• 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).

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

• 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/

Framework: MITRE ATT&CK

• 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/