Old iMessage Bug Causes iPhone To Crash With A Single Message
but don't worry just yet. You need to have a criteria in place for the iMessage bug to cause your phone to crash just from the act of receiving a message.
If someone sends you the below string of Arabic characters via SMS or iMessage, it can cause the Messages app to stop working and can take down the phone entirely if it appears in a lock screen notification.
لُلُصّبُلُلصّبُررً ॣ ॣh ॣ ॣ 冗
The bug appears to be related to how iOS processes Unicode text for banner notifications using the CoreText API.
It affects iOS 7 and iOS 8 right now and the only fix is to send a photo or piece of text to the original sender using the share sheet in another app.
This isn’t the first time a Unicode bug has affected iOS in this exact way. Apple is reportedly aware of the issue and is already working on a fix.