A PUK code for a SIM card, which stands for Personal Unblocking Key, is an eight-digit code that enables a blocked SIM card to be unlocked.

PUK is the code required to unlock a GSM SIM card that has disabled itself after an incorrect PIN code was entered 3-5 times in a row. If an incorrect PUK code is entered a certain number of times ...

After changing the SIM, you will be prompted to “Enter SIM PIN.” After three incorrect PIN attempts, users are prompted to enter the PUK code, which you should know because it’s your SIM card.

The attacker could just swap the SIM in the victim’s device, and perform the exploit with a SIM card that had a PIN lock and for which the attacker knew the correct PUK code.