PassFilter

Important

This was a very simple dll I wrote for a client in a dfir situation. Since then, I found out about Lithnet Password Protection for Active Directory which is what I would suggest you look into.

PassFilter is a dll that can be loaded into LSASS to filter passwords which are included in an offline HIBP file. This dll expects a binary version of the sha1 hash ordered txt from HIBP. You may convert the file using my convertHIBP tool. This dll is perfect for usage on domain controlles, since they should not be allowed to speak to the internet if possible at all.

Building

git clone https://github.com/fblz/convertHIBP.git

Then open PassFilter.sln in Visual Studio and build the PassFilter project in Release x64 mode.

Installation

For more or less up2date instructions see the official Microsoft documentation.

Get a binary hibp file

git clone https://github.com/fblz/convertHIBP.git
cd convertHIBP
go build
./convertHIBP -InputFile ./pwned-passwords-sha1-ordered-by-hash-v7.txt -OutputFile ./hibp-v7.bin

Copy hibp-v7.bin onto every domain controller (DC), or place it on a share that all DCs can reach. Since it's quite a big file, don't put it in SYSVOL.

Configure the hibp file

To point the dll to your local file, create the following registry key: Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Passfilter Under this key then create a REG_EXPAND_SZ property with name HashFile. Set its value to the full path of your hibp-v7.bin.

Install the dll

Grab x64\Release\PassFilter.dll from next to the PassFilter.sln. Place it into %WINDIR%\System32 on every DC.

Register the dll

To register the dllnavigate to the following registry path Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa then add the dll name PassFilter to the Notification Packages attribute.

Enable filtering

To finally enable the filtering, enable the password complexity policy. Either open Local Security Policy navigate to Account Policies\Password Policy and enable Password must meet complexity requirements or inside a group policy navigate to Computer Configuration\Policies\Windows Settings\Security Settings\Account Policies\Password Policy and enable Password must meet complexity requirements.

To complete the installation, restart the computer so LSASS can load the dll.