Welcome back, cyberwarriors!

In this part of the series, we’re looking at how PowerShell can cause serious damage when nothing is restricting it. We’ll show how it can slow systems down and knock them off completely. You’ll see how hardware interfaces can get disabled, license keys wiped and a blue screen forced with machines left unbootable.

All these techniques are destructive, but our goal here is to show you that you shouldn’t just monitor command execution in PowerShell, you should also experiment with Language Modes to limit the attack surface if a workstation gets compromised. If these scripts are misused in the wrong context, the results can be irreversible.

We’ll begin with the basics and then move toward the dangerous things. 

Overloading RAM

The loadram.ps1 script works by aggressively consuming system memory. It allocates large arrays until nearly all available RAM is exhausted, leaving only a small buffer so the OS does not immediately collapse. The machine becomes unusable and applications stop responding.

This type of attack can be used as a DoS tactic to slow down a server, or it can act as a distraction, while other activity takes place.

PS > .\loadram.ps1

Overloading CPU

The loadcpu.ps1 script applies the same principle to processor cores, pinning usage at 100% until the script is terminated. Just as with RAM exhaustion, this script can serve as a cover while hackers are doing something else.

PS > .\loadcpu.ps1

Windows License Killer

The license.ps1 script clears Windows product keys by wiping out OEM, retail and volume license entries from the registry. The system becomes stripped of activation data. After restarting the Software Protection Service, Windows will be unlicensed and may refuse to validate against Microsoft servers.

PS > .\license.ps1

Then you can check the product key:

PS > (Get-WmiObject -query 'select  from SoftwareLicensingService').OA3xOriginalProductKey

The result should be empty. 

USB and Network Killer

You can also kill network adapters and USB controllers using killer.ps1 script. Once you run it, the mouse and keyboard will stop working. There will be no way to transfer files, connect to the network or even plug in a recovery device without significant intervention.

PS > .\killer.ps1

Mayhem by PowerSploit

PowerSploit includes a module called Mayhem, which has two destructive PowerShell functions. These are Set-CriticalProcess and Set-MasterBootRecord. Both directly attack the operating system itself.

Set-CriticalProcess

Windows protects smss.exe and csrss.exe by marking them as critical. If they are terminated, the system triggers a Blue Screen of Death. Set-CriticalProcess can tag any process with this critical status. Killing it immediately forces a system crash.

To use it, first copy the Mayhem module from the repository to:

C:\Program Files\WindowsPowerShell\Modules\

Then you can run Set-CriticalProcess:

PS > Set-CriticalProcess

Confirm with Y and expect the machine to blue screen in moments.

Set-MasterBootRecord

This is the most destructive of all. Unlike Set-CriticalProcess, this attack corrupts the Master Boot Record (MBR), which is the first sector of the hard drive. The MBR has the bootloader and partition table and without it Windows cannot load.

When it’s overwritten, the system may only display your custom message and will refuse to boot into the OS. Some malware does the same. The OS will work only if you fix the MBR, but chances are you will have to reinstall the OS. 

In our article on Digital Forensics we were repairing a corrupted drive where the MBR had been overwritten.

PS > Set-MasterBootRecord -BootMessage 'Pwned by Cyber Cossacks!'

You can also force the system to reboot right after:

PS > Set-MasterBootRecord -BootMessage 'Pwned by Cyber Cossacks!' -Force -RebootImmediately

It will no longer boot into Windows.

Summary

We showed how far PowerShell can be pushed when used as a weapon. That alone should be enough to convince you to restrict its use and work with Language Modes to help protect your system. By default, workstations and servers are pretty permissive, which makes them comfortable to use. The same permissiveness is just as accommodating for a hacker who has breached a system through phishing. Restricted Language Mode is a must on workstations where users don’t need PowerShell in the first place.

Want to become a Powershell expert? Join our Powershell for Hackers training.

The post PowerShell for Hackers, Part 5: How to Crash and Burn Windows first appeared on Hackers Arise.