Looks like Wi-Fi networks with percent symbols in their names can cause an error
Network names can disable Wi-Fi on iPhones: A security researcher has discovered that some Wi-Fi networks with a percent symbol (%) in their name can disable Wi-Fi on iPhones and other iOS devices. Carl Shaw tweeted that if an iPhone comes within range of a network named %secretclub%power, the device won’t be able to use Wi-Fi or any related features, and even after resetting the network, the bug can continue to make the Wi-Fi on the device unusable.
A few weeks ago, Shaw and his Secret Club, a nonprofit group that reverse-engineers software for research purposes, discovered that if an iPhone connects to a network named SSiD %p%s%s%s%s%n, it causes a bug in the iOS network stack that disables Wi-Fi, and system network functions such as AirDrop become unusable.
9to5 Mac offered a possible explanation for this strange error:
The ‘%[character]’ syntax is commonly used in programming languages to format variables into an output string. In C, the ‘%n’ specifier means saving the number of characters written in the format string to a variable passed to the string formatting function. It’s probable that the Wi-Fi subsystem is passing Wi-Fi network name (SSID) in the unsanitized form to some internal library performing string formatting, which, in its turn, causes arbitrary writing to memory and buffer overflow. This will corrupt the memory and iOS watchdog will terminate the process, thereby effectively disabling Wi-Fi for the user.
We’ve reached out to Apple to see if it’s working on a fix, and we’ll let you know if we hear back from them. But as 9to5 Mac notes, the bug can be avoided by not connecting to Wi-Fi networks with percent symbols in their names.