A security researcher has found out that certain Wi-Fi networks names can disable Wi-Fi on iPhones and other iOS devices, such devices Wi-Fi may become unusable, i.e the device will not be able to use Wi-Fi / any related features even after resetting network settings.
According to the researcher, SSiDs with special characters especially those with per cent symbol (%) can disable Wi-Fi on iPhones and other iOS devices. A few weeks ago, security researcher Carl Schou and his not-for-profit group, Secret Club, which reverse-engineers software for research purposes, found that if an iPhone connected to a network with the SSiD name %p%s%s%s%s%n it would cause a bug in iOS’ networking stack that would disable its Wi-Fi, and system networking features like AirDrop would become unusable.
While responding to this claim, 9to5Mac, a news and review magazine for Apple products gave this possible explanation that the ‘%[character]’ syntax is commonly used in programming languages to format variables into an output string. In C, the ‘%n’ specifier means to save the number of characters written into the format string out to a variable passed to the string format function. The Wi-Fi subsystem probably passes the Wi-Fi network name (SSID) unsanitized to some internal library that is performing string formatting, which in turn causes an arbitrary memory write and buffer overflow. This will lead to memory corruption and the iOS watchdog will kill the process, hence effectively disabling Wi-Fi for the user.
The Magazine company concluded that the bug can likely be avoided by not connecting to Wi-Fi networks with per cent symbols in their names.