Jailbreaking iPhone 5
There are various custom firmware available for Jailbreaking iPhone 5 running iOS 10.3.3.

I'd direct you to releases section of the iOS Jailbreaking Wikipedia page to see the available firmware for yourself.

A few supported ones for your device (from the aforementioned Wikipedia page) are:


h3lix Jailbreak
EtasonJB
Poenix Jailbreak


Note: I personally do not Jailbreak my iOS devices. Please proceed at your own caution. A Jailbreak can be reverted any time by restoring the original firmware.