An issue was discovered on OnePlus One, X, 2, 3, and 3T devices. Due to a lenient updater-script in the OnePlus OTA images, and the fact that both ROMs use the same OTA verification keys, attackers can install HydrogenOS over OxygenOS and vice versa, even on locked bootloaders, which allows for exploitation of vulnerabilities patched on one image but not on the other, in addition to expansion of the attack surface. This vulnerability can be exploited by Man-in-the-Middle (MiTM) attackers targeting the update process. This is possible because the update transaction does not occur over TLS (CVE-2016-10370). In addition, physical attackers can reboot the phone into recovery, and then use \'adb sideload\' to push the OTA (on OnePlus 3/3T \'Secure Start-up\' must be off).