Previewed at WWDC, launching in the fall.
New iOS Bug Crashing iPhones Simply by Receiving a Text Message [Includes Fix]
Sending the string of characters to an iPhone results in an immediate respring, causing an iPhone to crash and quickly reboot. From there, if the Messages app was opened at a list view, the Messages app crashes automatically when you try to open it. If it was opened to the conversation where you received the message, the app will open, but attempting to go to another conversation causes Messages to crash.
MacRumors tested the bug on iPhones running iOS 8.3, but it may also be affecting other versions of iOS.
If you receive one of these messages, there are a few possible fixes that have worked for us and for other people who have encountered the bug. If the Messages app was opened to the conversation with the person who sent the offending message, the Messages app can be reopened to this conversation. Sending a reply message fixes the problem.
If Messages was opened to the conversation list view, the app will crash when you attempt to open it. You can fix this by having someone send you a message or by sending a message to yourself. There are several options for sending a message to yourself, including sending yourself a message via Siri or through the Share sheet in any app.
To send yourself a message in Siri, tell Siri to "Send a message to myself." Siri will open up a dialogue where you can give her a quick message like "Fix" that'll be sent to your iPhone to clear away the malicious message.
Alternatively, you can open an app like Notes, craft a quick note, and use the Share option (the little document with an arrow) to message it to yourself. Sending yourself something though the share sheet of an app opens a new messages window where you can enter your own contact information.
According to a Twitter user who spoke to Apple support, Apple's engineers are aware of the problem and are working on a fix.
Update: Apple has provided a brief official statement to iMore:
We are aware of an iMessage issue caused by a specific series of unicode characters and we will make a fix available in a software update.