ATT has a lot of bootlocked phones. The Wikileaks #Vault7 release has instructions to bypass this in the Cadmium document.
Cadmium is an exploit targeting a vulnerability in the Exynos Android bootloader which enables the persistent booting of an unsigned Android boot image. This document will cover the details of the Exynos bootloader vulnerability, how Cadmium exploits this vulnerability, and how one can port Cadmium to different devices/firmwares.
ATT has a lot of bootlocked phones. The Wikileaks #Vault7 release has instructions to bypass this in the Cadmium document.
Will Heimdall be able to make use of this?
https://security.stackexchange.com/questions/153225/does-cadmium-in-vault7-enable-custom-roms-on-all-atts-samsung-phones