Techniques
Sample rules
Windows AD AdminSDHolder ACL Modified
- source: splunk
- technicques:
- T1546
Description
The following analytic detects modifications to the Access Control List (ACL) of the AdminSDHolder object in a Windows domain, specifically the addition of new rules. It leverages EventCode 5136 from the Security Event Log, focusing on changes to the nTSecurityDescriptor attribute. This activity is significant because the AdminSDHolder object secures privileged group members, and unauthorized changes can allow attackers to establish persistence and escalate privileges. If confirmed malicious, this could enable an attacker to control domain-level permissions, compromising the entire Active Directory environment.
Detection logic
`wineventlog_security` EventCode=5136 ObjectClass=container ObjectDN="CN=AdminSDHolder,CN=System*"
| 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
| rex field=old_value max_match=10000 "\((?P<old_values>.*?)\)"
| rex field=new_value max_match=10000 "\((?P<new_ace>.*?)\)"
| mvexpand new_ace
| where NOT new_ace IN (old_values)
| rex field=new_ace "(?P<aceType>.*?);(?P<aceFlags>.*?);(?P<aceAccessRights>.*?);(?P<aceObjectGuid>.*?);(?P<aceInheritedTypeGuid>.*?);(?P<aceSid>.*?)$"
| rex max_match=100 field=aceAccessRights "(?P<AccessRights>[A-Z]{2})"
| rex max_match=100 field=aceFlags "(?P<aceFlags>[A-Z]{2})"
| lookup msad_guid_lookup guid as aceObjectGuid OUTPUT displayName as ControlAccessRights
| lookup ace_access_rights_lookup access_rights_string as AccessRights OUTPUT access_rights_value
| lookup ace_type_lookup ace_type_string as aceType OUTPUT ace_type_value
| lookup ace_flag_lookup flag_string as aceFlags OUTPUT flag_value as ace_flag_value ``` Optional SID resolution lookups
| lookup identity_lookup_expanded objectSid as aceSid OUTPUT downLevelDomainName as user
| lookup admon_groups_def objectSid as aceSid OUTPUT cn as group```
| lookup builtin_groups_lookup builtin_group_string as aceSid OUTPUTNEW builtin_group_name as builtin_group
| 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)
| 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
| eval aceControlAccessRights=if(mvcount(aceControlAccessRights)=1 AND aceControlAccessRights="","All rights",'aceControlAccessRights')
| search NOT aceType IN (*denied*,D,OD,XD) AND aceAccessRights IN ("Full control","All extended rights","All validated writes","Create all child objects","Delete all child objects","Delete subtree","Delete","Modify permissions","Modify owner","Write all properties",CC,CR,DC,DT,SD,SW,WD,WO,WP)
| `windows_ad_adminsdholder_acl_modified_filter`