Device Guard - Fixing VMWare Tools
I've been really keen to try Device Guard out lately and I finally rolled up my sleeves and used Matt Graeber's excellent guide found at:
All this work is based on his work and full credit goes to him. I wanted to write this post in case someone finds themselves in the same situation I was in; simply wanting to get familiarized with Device Guard using their own mini home lab. Using VMWare Workstation with Device Guard won't enable every feature available in Device Guard, but it's a good starting point to get familiar with deploying policies and just getting a general feel for the technology.
After following Matt's guide - VMWare tools refused to function and I want to outline how I got them working again using his posts and some Microsoft documentation.
I'm going to start off assuming you have followed Matt's steps and have a system deployed with Device Guard but with VMWare Tools in a non working state. The culprit, it seems, is sigc-2.0.dll
It looks like that particular dll isn't signed which doesn't jive with our originally created policies.
From this point we have to create a new policy specifically for VMWare tools which we will merge with our master policy. I used the following code:
$VMWareFiles = Get-SystemDriver -ScanPath 'C:\Program Files\VMware\VMware Tools' -UserPEs
New-CIPolicy -FilePath C:\DGPolicyFiles\VMWare.xml -DriverFiles $VMWareFiles -Level Publisher -Fallback Hash -UserPEs
This first line sets a variable with our scan path and then uses the New-CIPolicy cmdlet to create a policy using the publisher CA and then file hashes as a fallback method to generate a CI Policy.
Taking a peak at the policy that was generated, we see hashes generated for the various dll's within the VMWare tools folder, including our sigc-2.0.dll:
Now that we have a policy generated, we need to merge it into our master policy, I used the following code:
$CIPolicyPath = "C:\DGPolicyFiles\"
$MasterPolicy = $CIPolicyPath+"MergedAuditPolicy.xml"
$NewPolicy = $CIPolicyPath+"VMWare.xml"
Merge-CIPolicy -PolicyPaths $MasterPolicy,$NewPolicy -OutputFilePath $CIPolicyPath\MasterMergedVMWareRules.xml
This simply sets some variables with our path, including the original policy we used and our new VMWare Tools policy, the Merge-CIPolicy cmdlet is used to merge the two policies into one "Master Merged" policy. We then need to convert this policy and apply it, here I used Matt's code again, from his "Phase #4" portion ( http://www.exploit-monday.com/2016/09/introduction-to-windows-device-guard.html ) - I just changed the relevant variable in the following line:
$MergedAuditPolicyXml = Join-Path -Path $PolicyDirectory -ChildPath 'MasterMergedVMWareRules.xml'
Now after a reboot, you should have a working set of VMWare tools.
A few notes ...
- You should take a close look to see what the generated VMWare Tools policy looks like and if you are comfortable trusting the dll's and exe's whitelisted.
- I am by no means an expert in Device Guard, I just really wanted to get a feel for it because it's a pretty awesome way to secure your assets and it's free. I'm sure there are more streamlined ways to script this or to lock down the policy tighter.
- Perhaps using hashes isn't the most robust or secure way to build a whitelist policy, but I couldn't seem to get VMWare tools working using just the publisher CA level.
- Again, all credit goes to Matt Graeber for writing the original guides.
Some helpful links:
Last modified 3yr ago