A security researcher discovered that attempting to connect to Wi-Fi networks named “%p%s%s%s%s%n” causes iPhone and iPads’ wifi connections to be permanently disabled.
What exactly caused this bug is unknown, and Apple has yet to comment on it. There are, however, some theories as to why this bug occurs. According to 9to5Mac:
"Here’s the likely explanation: 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."
If you encounter this bug, you can restore your iPhone‘s or iPad‘s Wi-Fi connection by resetting your phone’s or toad’s network settings. This is done by going to Settings -> General -> Reset -> Reset Network.