This is a nice change of pace - for once, I get to write about a Flash exploit that is not related to Adobe screwing something up. Instead, this Flash vulnerability doesn't even have anything to do with Adobe's product, but instead a version of SMS called Flash SMS.
For those who are unaware, Flash SMS, or Class 0 SMS, is a standard that allows for displaying a message directly on a device's screen without being stored in the device's permanent memory. The message is then dismissible or savable. What the original intent for this type of messaging might have been is unclear, but its current usage is far from.
As it turns out, on the Nexus series of devices, a fairly small collection of these messages, 30 or so, can cause the phone to act erratically. This behavior is probably caused by the way the OS handles displaying them: semi-transparent black background with the text in the middle. When many of these semi-transparent boxes stack up, the phone could get overwhelmed in calculating display depth.
So, what do these devices do when they panic? In general, they reboot without warning. If the phone has a SIM card lock, then these phones will sit idle, waiting for user input on a screen that they do not know is waiting for them. This, of course, prevents the phone from receiving phone calls, texts or emails while waiting for the input, making the device fairly useless.
If you are completely unlucky, though, you might experience a different issue. On some occasions, instead of rebooting, the phone will just disconnect from the network. Of course this has the same effect as the previous, not receiving phone calls, texts or emails, but with the added bonus of not requiring a SIM lock.
This exploit exists on all versions of Android 4.x residing on Galaxy Nexus, Nexus 4 and Nexus 5 devices. Hopefully Google will figure out how to fix this as it could pose a fairly big issue considering it only requires a few special texts to sink the device. Not what I would want advertised as part of the "pure Google experience."