Carl Schou, a security researcher has discovered specific WiFi network names that will disable WiFi connectivity and related functions on iPhones.
— Carl Schou (@vm_call) July 4, 2021
According to the twitter post of Carl Schou, using the network name %secretclub%power will disable the WiFi connectivity of iPhones including features like AirDrop. The problem will even persist after resetting the iPhone’s network settings. Only a hard reset of the device will fix the issue.
He has also discovered previously that naming a WiFi network %p%s%s%s%s%n will also have the same effect but issues is slightly easier to fix as it only needs a network settings reset.
According to 9to5mac “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.”
Apple has yet to issue a fix or a statement for this issue. As of now, the safest course might be to avoid WiFi networks that sport the % character on their SSIDs.