An information security expert has discovered that some Wi-Fi networks with a percentage symbol (%) in their names can disable Wi-Fi on iPhones and other iOS devices, Carl Schou tweeted that if the iPhone is within range of a network called %secretclub% power, the device will not be able to use Wi-Fi or any related features, and even after resetting the network settings, the error may still show Wi-Fi on the device is unusable.
A few weeks ago, Schou and his nonprofit group, Secret Club, which reverses engineered software for research, discovered that if an iPhone connects to a network named SSID %p%s%s%s%s%n it might cause an error in the iOS networking stack that It may disable its Wi-Fi, and system network features such as AirDrop will become unusable.
9to5 Mac offered a possible explanation for the strange bug:
The "%[character]" syntax is commonly used in programming languages to format variables into an output string. In C, the delimiter "% n" means that the number of characters written in the format string is saved to a variable passed to the string format function.
The Wi-Fi subsystem may pass the uncorrected Wi-Fi name (SSID) to some internal library that formats the string, which in turn will write RAM and overflow the buffer, this will corrupt the memory and the iOS controller will stop operation, thus effectively disabling the user's Wi-Fi network.
As 9to5 Mac notes, the error can most likely be avoided by not connecting to Wi-Fi networks with percentage symbols in their names.