Its been over a year since I threw together the original Get-GPPPassword on a short flight and I was really having a hard time even looking at the code. In addition to a nagging bug, it needed to be rewritten and updated to include all the great recommendations from you guys. Its amazing how often I still see local passwords being enforced with Group Policy preferences. For some reason it actually feels like the problem is getting worse even with Microsoft's blatant warnings in Server 2012. The other issue that I have seen is that when administrators stop using preferences, the old XML file is not deleted. On more than one engagement I have found an old password which helped me guess the current one. We need to keep hammering at this poor practice.
Additionally, one of the things that jumped out at me while reworking this script is the simplicity of this task in PowerShell. Compared to accomplishing the same task in Ruby, PowerShell's XML parsing really gives it an edge. A lot of security professionals could benefit by spending a few days to learn it and Carlos Perez is teaching an awesome class at Derbycon!
General flow, performance and bug fixes including better error handling and a fix for the problem with how the base64-encoded string was being padded.
Support for parsing not only groups.xml, but also scheduledtasks.xml, services.xml and datasources.xml. The original post that inspired me to write the function appears to be down, but there have been other posts that point out that passwords can be stored in other Group Policy preference files as well. I attempted to create each one of those XML files and created logic for the 4 that seem used.
Ryan Ries pointed out that the script could easily be pointed at the domain controller which removes the need for any parameters and makes the script easier to run:
I broke out the decryption function (Get-DecryptedCPassword) If you want to decrypt a password offline, you can use that.
As always, the most current version of the Get-GPPPassword is available from the PowerSploit Github page. Thanks for reading, keep the comments and recommendations coming and join Skip Duckwall and I at BlackHat where we will briefly discuss Group Policy preferences in relation to the Pass-the-Hash attack with practical mitigation techniques.