#BugAlert: Percentage symbols in network names could brick iPhone's Wi-Fi
Last month, a zero-day vulnerability for iPhones was unearthed by Denmark-based security researcher Carl Schou. He tweeted that his iPhone's Wi-Fi functionality was permanently disabled after joining a specific network. In a recent development, he revealed that some wireless network names (called SSIDs) can permanently brick the iPhone's Wi-Fi with no known method to reverse the damage. Here's how to keep your iPhone safe.
Late in June, Schou discovered that joining a Wi-Fi network with an SSID (Service Set Identifier) containing many "%" symbols instantly disabled all Wi-Fi functionality on the iPhone. After connecting to a public network with SSID "%p%s%s%s%s%n" Schou's device failed to connect to any other Wi-Fi network and internet-based features like AirDrop also didn't work. The issue was observed on iPads as well.
On July 4, Schou tweeted that another public Wi-Fi SSID "%secretclub%power" also had the same effect where the iPhone's Wi-Fi was permanently disabled. Resetting the network settings didn't restore connectivity. 9to5Mac's possible explanation suggests that the Wi-Fi subsystem passes the SSID unsanitized to an internal iOS library that performs string formatting, which in turn uses an arbitrary memory to write and buffer overflow.
The explanation ties into the fact that the "%[character]" syntax is used for format specifiers in programming languages. 9to5Mac's explanation suggests that the Wi-Fi name could cause memory corruption on the iPhone, so the iOS watchdog kills the process, disabling Wi-Fi for the user in the process. This also seems to explain why resetting the network settings did not fix the problem.
Surprisingly though, this problem won't brick Wi-Fi on all iPhones. Some Reddit users managed to return to safety with an ordinary error message. So far, Apple has not commented on this vulnerability. Until a proper fix is released, we would strongly advise you to steer clear of Wi-Fi networks that have percentage symbols in their name.