There is a bug that makes it relatively easy for someone to cause Wi-Fi issues on iOS devices. All it takes, according to security researcher Carl Schou, is to create a public Wi-Fi hotspot with a specially crafted name, and when someone with an iOS device connects to it, their Wi-Fi is disabled.
Schou first mentioned the problem on Twitter on June 19. When an iOS device connects to a Wi-Fi network named “%p%s%s%s%s%n” its Wi-Fi is disabled. According to other people’s comments, what happens next can be quite different, depending on unknown factors:
Some users were able to reactivate Wi-Fi on their devices simply by resetting network settings. This didn’t work for others, including Schou, and neither did restarting the iPhone.
Several outlets, including 9to5Mac, covered the story at the time. The bug appears to be related to the syntax of some programming languages, where “% (character)” is a string format specifier.
It’s a fairly common type of bug in which a character string used in programming ends up in a place where it can cause problems, causing an app to crash.
As others experimented with the bug, it was discovered that other network names can be used to produce the same effect; Schou proposed “%secretclub%power”, and Security researcher Alex Skalozub, who spoke with The Register, said a name like “%Free %Coffee at %Starbucks” would also work.
— Carl Schou (@vm_call) July 4, 2021
This exacerbates the problem, as it’s relatively simple to create a Wi-Fi network name that sounds like something you’d want to connect to. Though it doesn’t appear that the bug can be used to steal your data or anything nefarious.
A prankster could set up a public Wi-Fi network that would mess up the iPhones of everyone who connected to it — and with the right name, it could take in a large number of people.
Schou’s Sunday tweet that he still hasn’t been able to fix his Wi-Fi brought this story back to life. He eventually got around it by manually editing an iPhone backup and removing the offending Wi-Fi network names from the “known networks” list.
plist — something that the average iPhone user is unlikely to do. Another user suggests deleting the offending Wi-Fi network name from the Mac’s iCloud Keychain.
While it’s reassuring to know that a fix for this bug exists, it’d be even better if Apple fixed it. Schou claims he contacted Apple about the problem but has not received a response. We’ve done the same and will update this article as soon as Apple responds.