GPP Passwords (Group Policy Preferences)
SYSVOL is a shared folder on all Domain Controllers that stores logon scripts and Group Policy data.
GPP (introduced in Windows Server 2008) allowed storing credentials (usernames + encrypted passwords) in XML files for things like scheduled tasks.
These XML files are stored in: <DOMAIN>\SYSVOL<DOMAIN>\Policies
The encryption key used is the same for all AD environments and was made public by Microsoft.
Because Authenticated Users (including normal users and computers) can read SYSVOL, anyone can access and decrypt the stored passwords.
This is now the encrypted pass looks like: ![[enc pass.png]]
Attack
To abuse GPP Passwords, we will use the Get-GPPPassword function from PowerSploit, which automatically parses all XML files in the Policies folder in SYSVOL, picking up those with the cpassword property and decrypting them once detected
Import GPPPassword
PS C:\Users\bob\Downloads> Import-Module .\Get-GPPPassword.ps1Execute GPPPasword
PS C:\Users\bob\Downloads> Get-GPPPasswordPrevention
In 2014, Microsoft released patch KB2962486 to stop storing passwords in GPP.
Patched systems won't store new passwords, but old ones may still exist.
Many AD environments, even after 2015, still have credentials in SYSVOL.
Important: The patch does not remove existing passwords, only blocks new ones.
Regularly check and clean SYSVOL to ensure no credentials are exposed.
Detection
There is no need for anyone to open the XML file that contains the creds, so if someone does, an event will be created.
EventID 4663
Or we can set logon types (
4624(successful logon),4625(failed logon), or4768(TGT requested)) based if the password is up to date or not
Honeypot
We can use the SYSVOL share for a trap set-up.
A semi-privileged use with a wrong password
Service account passwords are often old and rarely changed.
If the GPP file is newer than the last password change, the password is likely still valid.
If the password changed after the file was modified, it probably won’t work.
Run a dummy task with the account to generate recent login activity.
4771: failed pre-authentiaction 4776: bad password
Tasks
Task 1
Connect to the target and run the Powersploit Get-GPPPassword function. What is the password of the svc-iis user?
When we run the import module command we will get and error, this is a security feature of windows that restricts script executions. We bypass it with the command below
Now we import and execute the script
Answer: abcd@123
Task 2
After running the previous attack, connect to DC1 (172.16.18.3) as 'htb-student:HTB_@cademy_stdnt!' and look at the logs in Event Viewer. What is the Access Mask of the generated events?
From windows RDP connect and go to EventView Enter in the Security logs in filter the event ID 4663 and search the Details for access mask
Answer: 0X80
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