Recently, a simple script has been presented that can help someone to brick a computer in case of emergency. This script was defined as a switch killer, but what is a switch killer?

A switch killer refers to the main characteristic of this script, which turns off a computer by inserting or removing a USB stick from a port. This starts an immediate shutdown. This script is not very helpful for a penetration tester or white hat, but it can save someone in case of emergency.

Why USBkill?

Usually when police come to arrest a criminal, the first option for him is to completely wipe the devices that he is using. If he is successful, life for the forensic investigator becomes hard.

During the seizure, police start to analyze the criminal’s computer and will use some blocking device to prevent standby or screensaver password using a little USB device called mouse jiggler that emulates keyboard and mouse movements.

The official author’s reasons are:

  • In case the police or other thugs come busting in (or steal your laptop from you when you are at a public library as happened to Ross). Police commonly use a « mouse jiggler » to keep the screensaver and sleep mode from activating.
  • You don’t want someone to install backdoors or malware on your computer or to retrieve documents from your computer via USB.
  • You want to improve the security of your (Full Disk Encrypted) home or corporate server (e.g. Your Raspberry).

Mouse jigglers aren’t banned. You can find them on Amazon for few dollars (http://www.amazon.com/Cru-dataport-Jiggler-Automatic-keyboard-Activity/dp/B00MTZY7Y4/ref=pd_bxgy_pc_text_y/190-3944818-7671348).

How it works?

UsbKill is a simply python script composed by few lines of code and can be downloaded here:

If we take a look inside, it does no more than a loop control with lsusb waiting trigger event on USB port. If something changes on current state of USB configurations as unplugged or plug USB stick, it shuts down your computer abruptly.

Features:

  • Compatibility with Linux, *BSD and OS X
  • Shutdown the computer when there is USB activity
  • Ability to whitelist a USB device
  • Ability to change the check interval (default: 0.5)
  • Work perfectly in sleep mode (OS X)
  • Low memory consumption
  • No dependency except Python

Obviously, it is important to use a full disk encryption and wiping of RAM during the shutdown on your device or computer. Otherwise, this script is totally useless.

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How was it born?

The USBkill project was born from a real case happening to Ross Ulbricht, a famous criminal owner of Silk Road. Silk Road was an onion website that sold drugs. The FBI, during the operation to arrest him, applied a smart strategy to catch Ross logged into Silk Road with admin privileges.

The downside

This script is simple but has critical points to improve.

  • Root privilege for the execution.
  • Impossibility to check USB plugged at startup. If we plug in a USB stick at startup it will put into a whitelist.
  • Need of full disk encryption, otherwise it will be useless.
  • Wiping RAM during shutdown for preventing cold boot attack.

Conclusion

We need to remember that USBkill is not a antiforensic tool as the author disclaims. This tool is a trap for cops that don’t know the defense of your computer and has to be used as it is.

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