French security researcher Robert Baptiste, aka "Elliot Alderson," aka @fs0c131y, says he has found a way to temporarily "brick" any recent Samsung phone or tablet by forcing it to lock the Knox secure container and bouncing the user back to the launcher screen.
Baptiste says a malicious app, such as one he wrote as a proof of concept and posted on Github, could use two lines of code to change a couple of unprotected parameters in another Samsung system app to interfere with the Knox system.
"The device will be inoperable due to this local DoS [denial of service]," Baptiste wrote in a blog post. "Every time the victim will open the [Knox] SecureFolder app, the container will be locked and every time he will try to use his phone, the phone will come back directly to the first page of the launcher."
That's not really bricking the device, as it will still work — you just won't be able to use it. Baptiste said on Twitter that the malicious app, or indeed any user with physical access to the device, would not need administrative rights to carry out this attack.
You can get around this problem by rebooting into Safe Mode, which may be why Samsung does not consider this a security issue, according to Baptiste. He said he reported the issue to Samsung in March, but the company apparently responded that it "considered this issue as no/little security impact."
Tom's Guide has reached out to Samsung for comment, and we will update this story when we receive a reply.
Samsung is correct that at the moment, you'd have to sideload an app capable of doing this onto a Samsung device, which would of course require physical access to the phone and a way past the device's lockscreen. But it would be pretty easy to put Baptiste's code into an otherwise innocuous-looking app, sneak the app into the Google Play app store and fool an authorized user into installing it.
To boot a Samsung phone or tablet into Safe Mode, power off the device, reboot it, then hold down the Volume Down button when the logo appears during the boot process. Safe Mode disables any apps that were not installed at the factory, so you'll be able to unlock the screen and remove the malicious app. You can exit Safe Mode with a normal reboot.
The Knox secure container was introduced with the Samsung Galaxy S4 in 2013 and has appeared on most Samsung Android and Tizen smartphones, tablets and smartwatches since then.