Detection: Windows AD DCShadow Privileges ACL Addition

Updated Date: 2023-11-10 ID: ae915743-1aa8-4a94-975c-8062ebc8b723 Author: Dean Luxton Type: TTP Product: Splunk Enterprise Security

Description

This detection identifies an Active Directory access-control list (ACL) modification event, which applies the minimum required extended rights to perform the DCShadow attack.

 1`wineventlog_security` EventCode=5136 ObjectClass=domainDNS  
 2| stats min(_time) as _time values(eval(if(OperationType=="%%14675",AttributeValue,null))) as old_value values(eval(if(OperationType=="%%14674",AttributeValue,null))) as new_value values(OperationType) as OperationType by ObjectClass ObjectDN OpCorrelationID src_user SubjectLogonId  
 3| rex field=old_value max_match=10000 "\((?P<old_values>.*?)\)"  
 4| rex field=new_value max_match=10000 "\((?P<new_ace>.*?)\)"  
 5| mvexpand new_ace 
 6| where NOT new_ace IN (old_values)  
 7| rex field=new_ace "(?P<aceType>.*?);(?P<aceFlags>.*?);(?P<aceAccessRights>.*?);(?P<aceObjectGuid>.*?);;(?P<aceSid>.*?)$" 
 8| search aceObjectGuid IN ("9923a32a-3607-11d2-b9be-0000f87a36b2","1131f6ab-9c07-11d1-f79f-00c04fc2dcd2","1131f6ac-9c07-11d1-f79f-00c04fc2dcd2") 
 9| rex max_match=100 field=aceAccessRights "(?P<AccessRights>[A-Z]{2})"  
10| rex max_match=100 field=aceFlags "(?P<aceFlags>[A-Z]{2})"  
11| lookup msad_guid_lookup guid as aceObjectGuid OUTPUT displayName as ControlAccessRights 
12| lookup ace_access_rights_lookup access_rights_string as AccessRights OUTPUT access_rights_value  
13| lookup ace_type_lookup ace_type_string as aceType OUTPUT ace_type_value  
14| lookup ace_flag_lookup flag_string as aceFlags OUTPUT flag_value as ace_flag_value ``` Optional SID resolution lookups 
15| lookup identity_lookup_expanded objectSid as aceSid OUTPUT downLevelDomainName as user  
16| lookup admon_groups_def objectSid as aceSid OUTPUT cn as group ``` 
17| lookup builtin_groups_lookup builtin_group_string  as aceSid OUTPUT builtin_group_name as builtin_group 
18| eval aceType=coalesce(ace_type_value,aceType), aceFlags=coalesce(ace_flag_value,"This object only"), aceAccessRights=if(aceAccessRights="CCDCLCSWRPWPDTLOCRSDRCWDWO","Full control",coalesce(access_rights_value,AccessRights)), aceControlAccessRights=coalesce(ControlAccessRights,aceObjectGuid), user=coalesce(user, group, builtin_group, aceSid) 
19| stats min(_time) as _time values(aceType) as aceType values(aceFlags) as aceFlags(inheritance) values(aceControlAccessRights) as aceControlAccessRights values(aceAccessRights) as aceAccessRights values(new_ace) as new_ace values(SubjectLogonId) as SubjectLogonId by ObjectClass ObjectDN src_user user 
20| search (aceControlAccessRights="Add/Remove Replica In Domain" AND aceControlAccessRights="Manage Replication Topology" AND aceControlAccessRights="Replication Synchronization") OR (aceControlAccessRights="9923a32a-3607-11d2-b9be-0000f87a36b2" AND aceControlAccessRights="1131f6ab-9c07-11d1-f79f-00c04fc2dcd2" AND aceControlAccessRights="1131f6ac-9c07-11d1-f79f-00c04fc2dcd2") 
21| `windows_ad_dcshadow_privileges_acl_addition_filter`

Data Source

Name Platform Sourcetype Source Supported App
N/A N/A N/A N/A N/A

Macros Used

Name Value
wineventlog_security eventtype=wineventlog_security OR Channel=security OR source=XmlWinEventLog:Security
windows_ad_dcshadow_privileges_acl_addition_filter search *
windows_ad_dcshadow_privileges_acl_addition_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK
+ Kill Chain Phases
+ NIST
+ CIS
- Threat Actors
ID Technique Tactic
T1484 Domain or Tenant Policy Modification Defense Evasion
T1207 Rogue Domain Controller Privilege Escalation
T1222.001 Windows File and Directory Permissions Modification Defense Evasion
KillChainPhase.EXPLOITAITON
NistCategory.DE_CM
Cis18Value.CIS_10
Wizard Spider

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting Value
Disabled true
Cron Schedule 0 * * * *
Earliest Time -70m@m
Latest Time -10m@m
Schedule Window auto
Creates Notable Yes
Rule Title %name%
Rule Description %description%
Notable Event Fields user, dest
Creates Risk Event True
This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

Ensure you are ingesting Active Directory audit logs - specifically event 5136. See lantern article in references for further on how to onboard AD audit data. Ensure the wineventlog_security macro is configured with the correct indexes and include lookups for SID resolution if evt_resolve_ad_obj is set to 0.

Known False Positives

Unknown

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
ACL modification Event Initiated by $src_user$ applying $user$ the minimum required extended rights to perform a DCShadow attack. 100 100 100
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

References

Detection Testing

Test Type Status Dataset Source Sourcetype
Validation ✅ Passing N/A N/A N/A
Unit ✅ Passing Dataset XmlWinEventLog:Security xmlwineventlog
Integration ✅ Passing Dataset XmlWinEventLog:Security xmlwineventlog

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 1