Detection: Windows AD Self DACL Assignment

Updated Date: 2023-12-18 ID: 16132445-da9f-4d03-ad44-56d717dcd67d Author: Dean Luxton Type: TTP Product: Splunk Enterprise Security

Description

Detect when a user creates a new DACL in AD for their own AD object.

 1`wineventlog_security` EventCode=5136  
 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<aceInheritedTypeGuid>.*?);(?P<aceSid>.*?)$"  
 8| rex max_match=100 field=aceAccessRights "(?P<AccessRights>[A-Z]{2})"  
 9| rex max_match=100 field=aceFlags "(?P<aceFlags>[A-Z]{2})"  
10| lookup ace_type_lookup ace_type_string as aceType OUTPUT ace_type_value as aceType  
11| lookup ace_flag_lookup flag_string as aceFlags OUTPUT flag_value as ace_flag_value  
12| lookup ace_access_rights_lookup access_rights_string as AccessRights OUTPUT access_rights_value  
13| lookup msad_guid_lookup guid as aceObjectGuid OUTPUT displayName as ControlAccessRights ``` Optional SID resolution lookups  
14| lookup identity_lookup_expanded objectSid as aceSid OUTPUT downLevelDomainName as user  
15| lookup admon_groups_def objectSid as aceSid OUTPUT cn as group  ``` 
16| lookup builtin_groups_lookup builtin_group_string as aceSid OUTPUT builtin_group_name as builtin_group  
17| eval aceType=coalesce(ace_type_value,aceType), aceInheritance=coalesce(ace_flag_value,"This object only"), aceAccessRights=if(aceAccessRights="CCDCLCSWRPWPDTLOCRSDRCWDWO","Full control",coalesce(access_rights_value,AccessRights)), aceControlAccessRights=if((ControlAccessRights="Write member" OR aceObjectGuid="bf9679c0-0de6-11d0-a285-00aa003049e2") AND (aceAccessRights="All validated writes" OR AccessRights="SW"),"Add/remove self as member",coalesce(ControlAccessRights,aceObjectGuid)), user=coalesce(user, group, builtin_group, aceSid)  
18| stats values(aceType) as aceType values(aceInheritance) as aceInheritance values(aceControlAccessRights) as aceControlAccessRights values(aceAccessRights) as aceAccessRights values(new_ace) as new_ace values(aceInheritedTypeGuid) as aceInheritedTypeGuid by _time ObjectClass ObjectDN src_user SubjectLogonId user OpCorrelationID  
19| eval aceControlAccessRights=if(mvcount(aceControlAccessRights)=1 AND aceControlAccessRights="","All rights",'aceControlAccessRights') 
20| rex field=user "\\\(?P<nt_user>.*?)$" 
21| where lower(src_user)=lower(nt_user) 
22| `windows_ad_self_dacl_assignment_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_self_dacl_assignment_filter search *
windows_ad_self_dacl_assignment_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
T1098 Account Manipulation Privilege Escalation
KillChainPhase.EXPLOITAITON
KillChainPhase.INSTALLATION
NistCategory.DE_CM
Cis18Value.CIS_10
APT3
APT41
APT5
Dragonfly
FIN13
HAFNIUM
Kimsuky
Lazarus Group
Magic Hound

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
$src_user$ has created a DACL on $ObjectDN$ to grant themselves $aceControlAccessRights$ across $aceAccessRights$ 80 80 100
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