Scheduled Task Execution at Scale via GPO

Elastic Stack Serverless Security

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

Rule type: query

Rule indices:

• winlogbeat-*
• logs-system.*

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
• https://twitter.com/menasec1/status/1106899890377052160
• https://github.com/SigmaHQ/sigma/blob/master/rules/windows/builtin/security/win_gpo_scheduledtasks.yml

Tags:

• Elastic
• Host
• Windows
• Threat Detection
• Privilege Escalation
• Active Directory
• has_guide

Version: 101

Rule authors:

• Elastic

Rule license: Elastic License v2

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).

(event.code: "5136" and winlog.event_data.AttributeLDAPDisplayName:("gPCMachineExtensionNames" or "gPCUserExtensionNames") and
   winlog.event_data.AttributeValue:(*CAB54552-DEEA-4691-817E-ED4A4D1AFC72* and *AADCED64-746C-4633-A97C-D61349046527*))
or
(event.code: "5145" and winlog.event_data.ShareName: "\\\\*\\SYSVOL" and winlog.event_data.RelativeTargetName: *ScheduledTasks.xml 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: 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 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/