Microsoft has confirmed that the bug in Windows Phone that allows an SMS message to disable the messaging app and reboot the phone is indeed legitimate and the company is actively investigating. Greg Sullivan, Senior product manager for the Windows Phone division at Microsoft, writes "We are aware of the issue and our engineering teams are examining it now. Once we have more details, we will take appropriate action to help ensure customers are protected."
Thankfully, the exact method for the exploit was not disclosed by WinRumors when it uncovered the issue and it doesn't appear that the issue is strictly security-related, so users should be able to relax while Microsoft looks into a fix. Hopefully it will come in the form of an over-the-air update and roll out to all devices in relatively short order. Microsoft has shown it can efficiently distribute a major OS update with Windows Phone 7.5, we'll see if it can do the same with a high priority bug fix.