AdminSDHolder
Theory
AdminSdHolder protects domain objects against permission changes. "AdminSdHolder" either refers to a domain object, a "worker code" or an operation depending on the context.
The operation consists in the PDC (Principal Domain Controller) Emulator restoring pre-set permissions for high-privilege users every 60 minutes. Understanding what DACLs/ACEs are and how to abuse them is a requirement to the understanding of this persistence technique (see Access Controls abuse).
The operation is conducted by a "worker code" called SDProp (Security Descriptor propagator).
SDProp propagates AdminSdHolder's DACL to every protected object every 60 minutes if their DACL is different.
The AdminSdHolder object is located at CN=AdminSdHolder,CN=SYSTEM,DC=DOMAIN,DC=LOCAL. For instance, the default AdminSdHolder object's DACL contains the following.
Authenticated Users: Read
SYSTEM: Full Control
Administrators: Modify
Domain Admins: ReadAndExecute
Enterprise Admins: ReadAndExecute
The default protected objects are the following.
members (possibly nested) of the following groups:
Account Operators,Administrators,Backup Operators,Domain Admins,Domain Controllers,Enterprise Admins,Print Operators,Read-only Domain Controllers,Replicator,Schema Admins,Server Operatorsthe following users:
Administrator,krbtgt
Practice
Once sufficient privileges are obtained, attackers can abuse AdminSdHolder to get persistence on the domain by modifying the AdminSdHolder object's DACL.
Let's say an attacker adds the following ACE to AdminSdHolder's DACL: attackercontrolleduser: Full Control.
At the next run of SDProp, attackercontrolleduser will have a GenericAll privilege over all protected objects (Domain Admins, Domain Controllers, and so on).
AdminSdHolder's DACL can then be inspected with the same utility.
Resources
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