Startup/Logon Script added to Group Policy Object

Elastic Stack Serverless Security

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

Rule type: query

Rule indices:

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

Severity: medium

Risk score: 47

Runs every: 5m

Searches indices from: None (https://www.elastic.co/guide/en/elasticsearch/reference/current/common-options.html#date-math[Date Math format], see also Additional look-back time)

Maximum alerts per execution: 100

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

Tags:

• Elastic
• Host
• Windows
• Threat Detection
• Privilege Escalation
• Active Directory
• Investigation Guide

Version: 104

Rule authors:

• Elastic

Rule license: Elastic License v2

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).

(
 event.code:5136 and winlog.event_data.AttributeLDAPDisplayName:(gPCMachineExtensionNames or gPCUserExtensionNames) and
   winlog.event_data.AttributeValue:(*42B5FAAE-6536-11D2-AE5A-0000F87571E3* and
                                      (*40B66650-4972-11D1-A7CA-0000F87571E3* or *40B6664F-4972-11D1-A7CA-0000F87571E3*))
)
or
(
 event.code:5145 and winlog.event_data.ShareName:\\\\*\\SYSVOL and
   winlog.event_data.RelativeTargetName:(*\\scripts.ini or *\\psscripts.ini) and
   (message:WriteData or winlog.event_data.AccessList:*%%4417*)
)

Framework: MITRE ATT&CKTM

• Tactic:

  • Name: Privilege Escalation
  • ID: TA0004
  • Reference URL: https://attack.mitre.org/tactics/TA0004/

• Technique:

  • Name: Domain 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/

• Technique:

  • Name: Boot or Logon Autostart Execution
  • ID: T1547
  • Reference URL: https://attack.mitre.org/techniques/T1547/