Why can this strange string of characters break your iPhone’s Wi-Fi?

A security researcher has discovered a strange bug in Apple iPhones. By asking them to join a Wi-Fi network named in a certain way, it is possible to break the wireless connection of the device. How is it possible ? Because of an old, old-fashioned bug.

A strange bug has been discovered in the operating system of iPhone June 18, 2021. It is possible to break the Wi-Fi connection of Apple smartphones by simply asking them to connect to an access point with a somewhat barbaric name.

If you connect your iPhone to a Wi-Fi network named “% p% s% s% s% s% n”, your phone will grind for a while, then turn off your Wi-Fi completely preventing you from restarting it or connecting to it. another network. The bug persists even if you activate or deactivate airplane mode or restart your mobile.

So don’t have fun experimenting with it if you’re not ready to debug next (we’ll explain how to do that below). A priori, the situation even affects iPhone on the latest version of iOS (14.4.6). We have however tested on the beta version of iOS 15 and our phone says “Unable to connect to the network” which seems to mean that Apple is aware of the problem and should not be too late to roll out a fix for the phones. under iOS 14.

An old-fashioned vulnerability

But why exactly is this funny character sequel crashing Apple phones? It is very likely that this is due to a misinterpretation of the telephone. The sign ” % Makes the phone believe that the name of the Wi-Fi network is a computer command to be executed and not some stupid Wi-Fi name.

Above all, do not connect to this kind of Wi-Fi network // Source: Photo Corentin Béchade for Numerama

More specifically, in the C programming language, the percent sign followed by a letter acts as a format specifier (string format specifiers in English). That is, a piece of code that actually tells the compiler – the program that transforms code created by humans (source code) into machine-readable code (object code) – to run a command. (here, write to the phone’s memory) instead of just joining the Wi-Fi network.

When the iPhone therefore tries to interpret the code present within the SSID, then the Wi-Fi crashes. This type of attack is called ” strings format type exploits ”, or ” Format String Vulnerabilities In English, and had its heyday decades ago, in the early 2000s.

The security researcher who discovered the bug does not hide it by the way, since he told the BleepingComputer site that all his devices were named in this way in order to ” rot devices developed with the feet“. Apple will appreciate it.

How to get your Wi-Fi back?

Let’s face it, there is little chance that you will encounter this bug on an unexpected basis. You already need a little knowledge to change the name of your Wi-Fi network and opposite, an iPhone owner would have to want to connect to this strange Wi-Fi. But as long as someone offers open Wi-Fi with that name in a public space, there is a way to gently break some iPhone.

The only way to recover your Wi-Fi connection after such a bug is to go to Settings then General, Reset, then Reset network settings. Your iPhone will then restart and the Wi-Fi will be functional again. However, you will have lost all Wi-Fi passwords saved in the phone, so be careful.

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