Finding Rogue KMS Servers in the Enterprise…

In larger Enterprises with Microsoft-based infrastructure, it’s highly likely that the licensing for the Windows 7 workstations will be based on the Microsoft KMS model.  If you don’t already know, this means you run servers in-house that register themselves into DNS as license providers, and Windows clients will learn of them (and become affiliated with them) to get a license, rather than contacting Microsoft themselves across the Internet.

Unfortunately, one problem that can occur is that someone who has access to the Microsoft license codes (like an I.T. worker, developer, etc.) might accidentally install a KMS license on a server that is not intended to be a KMS server.  And when a KMS license is installed, the server doesn’t know any better; and dutifully registers its KMS capability with the internal Active Directory based DNS as a VLMCS SRV record. 

Recently, I ran into a situation where I needed to hunt down and eliminate some accidentally rogue KMS servers that had cropped up across a large infrastructure, and be able to re-check at regular intervals.  While I originally wrote the script as a bash shell script for Linux, I re-wrote it into PowerShell recently for someone who asked, and I thought I’d post the new version here.

Mind you, this is a stripped-down version of the script, but it includes all that is needed to run the check manually for a hierarchical DNS infrastructure (although you may wish to strip out components if you just want to check the parent domain). 

Copy the contents below, paste them into a PowerShell script file (*.ps1), change the variables at the top… and have fun!

 

# Change the following 3 variables as needed.
# This script will loop through the subdomains, checking for KMS servers in each
# subdomain, and then at the parent domain.
$subs = @("subdomain1", "subdomain2", "etcetera")
$parentdomain = mydomain.local
$outfile = "checkKMS-Results.txt"
write "KMS check report..." | Out-File $outfile
write " " | Out-File $outfile -append
write "The only valid KMS servers are at the $parentdomain, as follows:" | Out-File $outfile -append
write "KMS1, KMS2, KMS3" | Out-File $outfile -append
write " " | Out-File $outfile -append
write "There should not be a KMS server at any of these locations:" | Out-File $outfile -append
foreach ($item in $subs)
{
  write "Checking subdomain: $item"
  $result = nslookup -type=srv _vlmcs._tcp.$item.$parentdomain. |findstr /C:"_vlmcs" /C:"svr hostname"
  if ("X$result" -eq "X")
  {
    write "No registered KMS server in $item" | Out-File $outfile -append
  }
  else
  {
    write "***KMS FOUND at this location: ***" | Out-File $outfile -append
    write $result | Out-File $outfile -append
  }
}
write " "  | Out-File $outfile -append
write "On the contrary, the following should be valid KMS servers:" | Out-File $outfile -append
$result = nslookup -type=srv _vlmcs._tcp.$parentdomain. |findstr /C:"_vlmcs" /C:"svr hostname"
$result | Out-File $outfile -append
write "...Done!" | Out-File $outfile -append

Enjoy!

🙂

 

2017-07-27T00:01:08+00:00 February 8th, 2012|Uncategorized|

About the Author:

Jeremy is just a regular guy that likes to occasionally tell the world about stuff.

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