Skip to main content

What Happens When You Run GPUpdate?

When you run gpupdate on a server, it looks like a simple command. But in the background, the server is actually following a strict seven-step process to get its new settings from the Domain Controller (DC).

Here is exactly what happens.

1. Starting the Service
When you type the command, it wakes up a specific background task called the Group Policy Client.

  • If you just run gpupdate, the server only asks for settings that have changed.
  • If you run gpupdate /force, the server ignores its history and re-downloads every single setting.

2. Finding a Domain Controller
The server needs to find a "source" for its settings. It checks your network’s DNS to find a Domain Controller. Once it finds one, it proves who it is (authenticates) using its computer account.
3. Figuring Out Which Policies Apply
The server asks the Domain Controller for a list of all Group Policy Objects (GPOs). It checks several things to see which ones it should actually use:

  • Location: Is the GPO linked to the server’s specific folder (OU) or domain?
  • Permissions: Does the server have permission to read and use that GPO?
  • Filters: Are there rules saying "only apply this to Windows Server 2022" or similar?

4. Checking for Version Changes
Every GPO has a version number. The server compares the version number on the Domain Controller to the one it already has saved.

  • If the number on the DC is higher, the server knows there is an update.
  • If the numbers match, the server usually skips that GPO (unless you used /force).

5. Downloading the Files
Once the server knows which GPOs are new, it connects to a shared folder on the Domain Controller called SYSVOL. It downloads the actual files, which contain the registry settings, scripts, or wallpaper paths.

The SYSVOL folder is physically located on every Domain Controller at C:\Windows\SYSVOL\sysvol, but member servers access it over the network using the path \\DomainName\SYSVOL. To get there, the member server uses its Computer Account to authenticate via Kerberos, proving it is a trusted part of the domain without needing a user to log in manually. It connects using the SMB (Server Message Block) protocol over Port 445, which is the standard way Windows shares files. Because SYSVOL uses DFS (Distributed File System), the server doesn't have to point to one specific Domain Controller; it simply asks the domain for the files, and Windows automatically connects it to the closest available DC to download the necessary Group Policy templates.

6. Applying the Settings
The main Group Policy engine doesn't actually change your settings. Instead, it hands the files over to "specialists" called Client-Side Extensions.

  • One specialist handles Registry changes.
  • Another handles Security rules (like who can log in).
  • Another handles Preferences (like mapping a network drive).

Think of the Group Policy engine as a project manager. It finds the instructions, but it doesn't do the physical labor. Instead, it hires "specialists" called Client-Side Extensions (CSEs) to do the actual work on the server.
Each specialist has one specific job they are trained for:

  • The Registry Specialist: This is the most common one. Its only job is to open the Windows Registry and change the settings you’ve picked, like disabling the Control Panel or setting a wallpaper.
  • The Security Specialist: This worker handles the "lock and key" settings. It decides which users are allowed to log in to the server and what they are allowed to do once they get in.
  • The Preferences Specialist: This one handles the "extras" that make a user's life easier, such as automatically connecting to a printer or making sure a specific folder appears on the desktop.

When the Group Policy engine finishes downloading the instruction files from the network, it calls these specialists one by one. It hands each of them the part of the file they understand. The specialists then go into the server's system, make the changes, and report back when they are done. This is why some settings (like security) might take a few seconds longer to apply than others. 

7. Finishing and Logging
After the specialists finish their work, the server saves the new version numbers so it knows it is up to date. It then records a "Success" message in the Windows Event Viewer so you can check it later.
If you want to see exactly which policies worked and which ones failed, run gpresult /r. This gives you a simple list of every policy applied during the update.

Required ports:

Port 53 (TCP/UDP): DNS – Used to find the Domain Controller.
Port 88 (TCP/UDP): Kerberos – Used to authenticate the computer account.
Port 135 (TCP): RPC Endpoint Mapper – Used to start the connection process.
Port 389 (TCP/UDP): LDAP – Used to search for the list of GPOs in Active Directory.
Port 445 (TCP): SMB – Used to download the policy files from the SYSVOL folder.
Ports 49152–65535 (TCP): RPC Dynamic Ports – Used to transfer the policy data.
 

Labels:

Popular Posts

RUST error: linker `link.exe` not found

While compiling Rust program in a windows environment, you may encounter the error : linker `link.exe` not found. This is because of the absence of the C++ build tools in your machine. For compiling Rust programs successfully, one of the prerequisites is the installation of the Build Tools for Visual Studio 2019.   Download the Visual Studio 2019 Build tools from the Microsoft website. After the download, while installing the Build tools, make sure that you install the required components (highlighted in Yellow) This will download around 1.2GB of required files. Once everything is successfully installed, reboot and re-run your rust program and it will compile successfully.   Read More on RUST Hello World Rust Program : Code explained RUST Cargo Package Manager Explained Data Representation in Rust.
Read more

Download Microsoft Office 2019 offline installer.

When you do malware analysis of documents or office files, it is important to have Microsoft Office installed in your Lab machine. I am using flare VM and it doesn't comes with MS Office. Since Microsoft is promoting Microsoft 365 over the offline version, finding the offline installer is not that easy. Here is the list of genuine Microsoft links to download the office .img files.  Download Microsoft Office 2019 Professional Plus : https://officecdn.microsoft.com/db/492350F6-3A01-4F97-B9C0-C7C6DDF67D60/media/en-US/ProPlus2019Retail.img Download Microsoft Office 2019 Professional : https://officecdn.microsoft.com/db/492350F6-3A01-4F97-B9C0-C7C6DDF67D60/media/en-US/Professional2019Retail.img Download Microsoft Office 2019 Home and Business : https://officecdn.microsoft.com/db/492350F6-3A01-4F97-B9C0-C7C6DDF67D60/media/en-US/HomeBusiness2019Retail.img Download Microsoft Office 2019 Home and Student : https://officecdn.microsoft.com/db/492350F6-3A01-4F97-B9C0-C7C6DDF67D60/media/en-U...
Read more

Cisco ASA: Disable SSLv3 and configure TLSv1.2.

For configuring TLS v1.2, the ASA should run software version 9.3(2) or later. In earlier versions of ASA, TLS 1.2 is not supported.If you are running the old version, it's time to upgrade. But before that i will show you the config prior to the change. I am running ASA version 9.6.1 Now ,set the server-version to tlsv1.2, though ASA supports version tlsv1.1, its always better to configure the connection to more secure. Server here in the sense, the ASA will be act as the server and the client will connect to the ASA.     #ssl server-version tlsv1.2 set the client-version to tlsv1.2, if required.     #ssl client-version tlsv1.2 ssl cipher command in ASA offers 5 predefined security levels and an additional custom level.     #ssl cipher tlsv1.2 high we can see the setting of each cipher levels using #show ssl cipher command. Now set the DH group to 24, which is the strongest offered as of now in the AS...
Read more

How to Install Netmiko on Windows?

Netmiko, developed by kirk Byers is an open source python library  based on Paramiko which simplifies SSH management to network devices and is primarily used for network automation tasks. Installing Netmiko in linux is a matter o f one single command but if you need to use Netmiko in your Windows PC, follow this process. 1) Install the latest version of Python. 2) Install Anaconda, which is an opensource distribution platform that you can install in Windows and other OS's (https://www.anaconda.com/download/) 3) From the Anaconda Shell, run “ conda install paramiko ”. 4) From the Anaconda Shell, run “ pip install scp ”. 5) Now Install the Git for Windows. (https://www.git-scm.com/downloads) . Git is required for downloading and cloning all the Netmiko library files from Github. 6) From Git Bash window, Clone Netmiko using the following command git clone https://github.com/ktbyers/netmiko&#8221         7) Onc...
Read more

PrintNightmare (CVE-2021-1675) PoC exploit Walkthrough

I am not an exploit developer but was interested to see how this vulnerability can be exploited. So i tried to replicate the infamous PrintNightmare vulnerability using the following PoCs ( https://github.com/cube0x0/CVE-2021-1675 ) and ( https://github.com/rapid7/metasploit-framework/pull/15385 ) However i had trouble with the new metasploit module (auxiliary/admin/dcerpc/cve_2021_1675_printnightmare) and i couldn't able to exploit the machine successfully. So i tried the second PoC from cube0x0. This one has done the magic. I just followed the guidelines with couple of tweaks. First of all, i installed the impacket (cube0x0 version) which will install the required modules and files. After that i set up a samba share with an anonymous login. This is required for hosting the dll file. I edited the smb.conf with the following settings. [global]     map to guest = Bad User     server role = standalone server     usershare allow guests = yes ...
Read more

Google Cloud : Basic Cloud Shell commands

Google Cloud resources can be managed in multiple ways. It can be done using Cloud Console, SDK or by using Cloud Shell. A few basic Google Cloud shell commands are listed below. 1)    List the active account name gcloud auth list 2)    List the project ID gcloud config list project 3)    Create a new instance using Gcloud shell gcloud compute instances create [INSTANCE_NAME] --machine-type n1-standard-2 --zone [ZONE_NAME] Use gcloud compute machine-types list to view a list of machine types available in particular zone. If the additional parameters, such as a zone is not specified, Google Cloud will use the information from your default project. To view the default project information, use gcloud compute project-info describe 4)    SSH in to the machine gcloud compute ssh [INSTANCE_NAME] --zone [YOUR_ZONE] 5)    RDP a windows server gcloud compute instances get-serial-port-output [INSTANCE_NAME...
Read more

Unable to locate package linux-headers / E: Unable to locate package linux-headers-5.10.0-kali5-amd64

While compiling programs, you may encounter this particular error. E: Unable to locate package linux-headers-5.10.0-kali5-amd64 I encountered this while compiling a C code. To fix this, i first updated my Kali machine (v2020.2a).  sudo apt update -y && apt upgrade -y && apt dist-upgrade   Rebooted. Then installed the headers.   sudo apt install linux-headers-$(uname -r)  
Read more