Grant rights

This abuse can be carried out when controlling an object that has WriteDacl over another object.

The attacker can write a new ACE to the target object’s DACL (Discretionary Access Control List). This can give the attacker full control of the target object.

Instead of giving full control, the same process can be applied to allow an object to DCSync by adding two ACEs with specific Extended Rights (DS-Replication-Get-Changes and DS-Replication-Get-Changes-All). Giving full control leads to the same thing since GenericAll includes all ExtendedRights, hence the two extended rights needed for DCSync to work.

Story time, Exchange Servers used to have WriteDacl over domain objects, allowing attackers to conduct a PrivExchange attack where control would be gained over an Exchange Server which would then be used to grant an attacker-controlled object DCSync privileges to the domain.

ACE inheritance

If attacker can write an ACE (WriteDacl) for a container or organisational unit (OU), if inheritance flags are added (0x01+ 0x02) to the ACE, and inheritance is enabled for an object in that container/OU, the ACE will be applied to it. By default, all the objects with AdminCount=0 will inherit ACEs from their parent container/OU.

Impacket's dacledit (Python) can be used with the -inheritance flag for that purpose (PR#1291).

UNIX-like

From UNIX-like systems, this can be done with Impacket's dacledit.py (Python).

⚠️ At the time of writing, May 2nd 2022, the Pull Request (#1291) is still pending.

# Give full control
dacledit.py -action 'write' -rights 'FullControl' -principal 'controlled_object' -target 'target_object' 'domain'/'user':'password'

# Give DCSync (DS-Replication-Get-Changes, DS-Replication-Get-Changes-All)
dacledit.py -action 'write' -rights 'DCSync' -principal 'controlled_object' -target 'target_object' 'domain'/'user':'password'

For a DCSync granting attack, instead of using dacledit, ntlmrelayx has the ability to operate that abuse with the --escalate-user option (see this).

To enable inheritance, the -inheritance switch can be added to the command. Then it is possible to find interesting targets with AdminCount=0in BloodHound for example, by looking at the object attributs.

# Give full control on the Users container with inheritance to the child object
dacledit.py -action 'write' -rights 'FullControl' -principal 'controlled_object' -target-dn 'CN=Users,DC=domain,DC=local' -inheritance 'domain'/'user':'password'

Alternatively, it can be achieved using bloodyAD

# Give full control (with inheritance to the child object if applicable)
bloodyAD --host "$DC_IP" -d "$DOMAIN" -u "$USER" -p "$PASSWORD" add genericAll $TargetObject $ControlledPrincipal

# Give DCSync (DS-Replication-Get-Changes, DS-Replication-Get-Changes-All)
bloodyAD --host "$DC_IP" -d "$DOMAIN" -u "$USER" -p "$PASSWORD" add dcsync $ControlledPrincipal

Windows

From a Windows system, this can be achieved with Add-DomainObjectAcl (PowerView module).

# Give full control
Add-DomainObjectAcl -Rights 'All' -TargetIdentity "target_object" -PrincipalIdentity "controlled_object"

# Give DCSync (DS-Replication-Get-Changes, DS-Replication-Get-Changes-All)
Add-DomainObjectAcl -Rights 'All' -TargetIdentity "target_object" -PrincipalIdentity "controlled_object"

A few tests showed the Add-DomainObjectAcl command needed to be run with the -Credential and -Domain options in order to work

Resources

Abusing Active Directory Permissions with PowerView - harmj0yharmj0y

DCSync: Dump Password Hashes from Domain ControllerRed Teaming Experiments