When the Messages app opens the message containing the vCard, it tries to open it and freezes displaying a white screen.
Below a video PoC of the vulnerability.
A researcher discovered that a single text message could be exploited to crash the Messages app by MMS on iOS due to a recently discovered bug
A single text message could be exploited to disable the Messages app on any iPhone due to a recently discovered bug.
The bug flaw makes the Apple Message app inoperable, making it impossible to read text messages or iMessages. The flaw is serious, the app will continue to crash even when the user closes it or reboot the device.
In order to exploit the flaw, it is necessary to send to the target device a vCard (a transferable Address Book contact) containing so many lines of code that the Messages app is not able to process.
Because the Messages app always tries to open the most recent text message when it is launched, it will continue trying to open the malicious message even when the app is closed or the whole phone is rebooted.
“When you click, iOS want to read the text, the text in the file is very complicated for the system and cause a CPU average: the app freeze. You close the app, want to reopen but iOS want to reload the previous message but can’t because it’s the vcf file.” reads the blog post published by vincedes3.
The bug is similar to the “Effective Power” discovered in May 2015, when users noticed that a text message containing a string of Arabic text would crash phones.
Back to the present, there is a good news for those users that have received the malicious message. There at least two workarounds to remove the message from the top of the inbox:
- By clicking this Fix link: vincedes3.com/save.html, it will open the window for sending a new message, pressing cancel and deleting the malicious message.
For devices (including iPad) where the fix link does not work, ask Siri to send a message to the victim and click on the text. pic.twitter.com/3id4Y8Lhkn
— vincedes3 (@vincedes3) 29 dicembre 2016
- By sending yourself a message in Siri, or ask someone else to send you a message. Once the message is received the Messages app will allow you to open the new message instead of the malicious one.
@vincedes3 pic.twitter.com/S37I4MVUPe
— Luca Marzano (@marzanoluca93) 30 dicembre 2016
