Arcticsn0w announced the PoC on reddit. It was created after users who were trying to follow dayt0n's bootcolor changing method (that messes with the device's nvram) reported completely bricked devices due to a misstep in following the instructions.
I have released a very, very, very, very dangerous package as a proof of concept called "KilliOS" on my personal Cydia repository (http://arcticsn0w.github.io). It is an empty package which messes with nvram values in the postinst script, and then forces a reboot. Installing this package will instantly kill your device.
Installation of the tweak results in "instant death of your device". Something which is stressed repeatedly by acticsn0w.
"TL;DR Be very careful. Please, I swear to god, do not install KilliOS. Please. If you do, I can't help you fix your device. It's very dangerous. It is only a proof of concept saying "Tweaks CAN do this". Do not install. Do not install. Do not install. Do not install. Do not install. Do not install. Do not install. Do not install. Do not install. Do not install. Do not install."
The tweak was eventually pulled because it was so dangerous and the code has been made available in GitHub.
All of this is based on changing a nvram variable called DClr_override.
If this is changed to an invalid value for the device (valid values are not the same on all devices), and the device is rebooted, the device will permanently not be able to boot. This cannot be fixed with a DFU restore or any other method.
DClr is the variable inside of iBoot that determines what color the Apple logo should be on boot, notes dayt0n. It only exists on the iPhone 5 and up. It is composed of 32 hex characters, consisting of 16 bytes, and it determines the color of the logo until SpringBoard begins to launch.
It's pretty simple to change the DClr value but some users attempting to follow the instructions discovered that a mistake led to the bricking of their device.
Now that a very simple method for bricking devices has been made public, users are in danger of installing a malicious tweak that can kill their device.
To protect yourself we strongly suggest that you only install tweaks from respected repositories and developers. Pirated tweaks and questionable repos could put your device at risk.
Thankfully developers are working on a fix and there is already a temporary failsafe by ktechmidas that offers some protection. More details here.
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