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Startup/Logon Script added to Group Policy Object

Detects the modification of Group Policy Objects (GPO) to add a startup/logon script to users or computer objects.

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:

Tags:

  • Domain: Endpoint
  • OS: Windows
  • Use Case: Threat Detection
  • Tactic: Privilege Escalation
  • 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 instruct arbitrarily large groups of clients to execute specified commands at startup, logon, shutdown, and logoff. This is done by creating or modifying the scripts.ini or psscripts.ini files. The scripts are stored in the following paths:

  • <GPOPath>\Machine\Scripts\
  • <GPOPath>\User\Scripts\
  • 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 legitimately authorized and executed under a change management process.
  • Group Policy Abuse for Privilege Addition - b9554892-5e0e-424b-83a0-5aef95aa43bf
  • Scheduled Task Execution at Scale via GPO - 15a8ba77-1c13-4274-88fe-6bd14133861e
  • 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 scripts 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 : "*42B5FAAE-6536-11D2-AE5A-0000F87571E3*" and
    winlog.event_data.AttributeValue : (
      "*40B66650-4972-11D1-A7CA-0000F87571E3*",
      "*40B6664F-4972-11D1-A7CA-0000F87571E3*"
    )
  ) or
  (
    winlog.event_data.ShareName : "\\\\*\\SYSVOL" and
    winlog.event_data.RelativeTargetName : ("*\\scripts.ini", "*\\psscripts.ini") and
    winlog.event_data.AccessList:"*%%4417*"
  )
)

Framework: MITRE ATT&CK