So far, the phenomenon is mainly known from messages on WhatsApp or Apple’s iMessage: sending certain cryptic character combinations can make the apps unusable. The equivalent for WiFi names that has now been discovered is significantly less complex in comparison, but even more effective.
You give your wifi the not very poetic name “%p%s%s%s%s%n” and connects an iPhone to the network, it switches off the WiFi function without comment. And even permanently: If you try to reactivate it via the settings, it is simply switched off again in a fraction of a second.
Even a restart does not fix this, the iPhone can neither be connected to a WLAN nor used for the Airdrop data transfer function. The only solution at the moment is to reset the network connections, how to do this is explained below.
Found the weak point by accident
The reaction to the bizarre network name was described by security researcher Carl Schou. He had found the bug by accident when connecting his iPhone XS to the unusually named WiFi, he said “Bleeping Computers”. When asked about the reason for choosing a name, he replied: “I use format strings of this kind for all devices. Sh *** badly developed devices.” The error can also be found in the current iOS version 14.6; the observed reaction could not be provoked on Android devices.
In fact, the character string in the iPhone system seems to trigger several errors, all of which work on the same principle, found out other experts. Put simply, brings the string “%n” in the network name causes the iPhone to develop an ever longer string of characters from it, until the program code for the network settings ultimately crashes. Because this happens again and again when the WLAN function is switched on, it switches itself off again immediately.
The only known solution is to reset network settings. The option can be found in the settings under “Generally” and “Reset to default”. After confirmation and a restart, the WiFi function should be usable again. Only one security researcher complained to Twitter that this would not have helped either.
Nevertheless, the error is probably not a real danger to the general public. On the one hand, the iPhone would have to be specifically logged into a WLAN named in this way; automatic logging into foreign networks is not possible with the iPhone. Even if it comes to logging in, the risk is probably limited to the failure of the WiFi connection: According to an analysis of the security blog “Chichou.me” the error cannot be used to run further malicious software on the device.
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