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GPP / cPassword Attacks

PreviousLNK File AttackNextMimikatz

Last updated 6 months ago

What Happened?

  • Group Policy Preferences (GPP) was a feature introduced in Windows Server 2008 to simplify the management of local accounts and services across domain-joined machines.

  • Admins could use GPP to:

    • Set passwords for local admin accounts.

    • Configure services and other tasks via Group Policies.

What Made GPP Vulnerable?

Here’s where things went wrong:

  • GPP allowed embedded credentials (e.g., local admin passwords) to be set within XML files.

  • These credentials were encrypted and stored as cPassword values in files like Groups.xml.

  • The Groups.xml file resides in SYSVOL – a shared folder on every domain controller that all authenticated users can access

The encryption should have kept these passwords safe, right? Well…

The OOPS Moment

Microsoft made a critical mistake:

  • The AES encryption key used to encrypt the cPassword was hardcoded.

  • Worse yet, they accidentally published this encryption key in official documentation.

  • Result? Anyone who gets access to the XML file can easily decrypt the cPassword.

https://n1chr0x.medium.com/unwrapping-gpp-exposing-the-cpassword-attack-vector-using-active-htb-machine-4d3b97e0ac43