OnePlus’ 3 and 3T flagships, it has been discovered, have been affected by a vulnerability that can open them up to all sorts of privilege escalation attacks, but the bug requires eitherphysical access to the device or remote access via the Android Debug Bridge (ADB). The bug occurs in the phone’s Fastboot mode, where a USB connection or a remote ADB connection can be used to issue a simple command to the device that will switch SElinux, a built-in Linux security protocol, from “Enforcing” to “Permissive.” Remote ADB requires the setting to be enabled in Developer Settings. The bug seemingly only exists in OnePlus’ stock firmware, and evidence suggests it’s a part of a development workaround. OnePlus has already been made aware of the issue and is looking into it.
While the bug actually being executed would require someone to leave their phone around or leave remote ADB turned on in an untrusted environment, once the switch has been flipped, many of Android’s built-in protections are disabled. Apps that try to gain root access and would usually be denied are granted, and internal protections that would normally deny a number of malicious actions let them slip through. Setting SELinux to “Permissive” is ordinarily reserved for development testing on a device as it’s usually only temporarily enabled by an experienced user for one reason or another and won’t persist across a reboot. With this exploit, however, the status will be retained across boot cycles.
The bug was uncovered and noted by a user on IBM’s X-Force security research team. Users have several options to patch the vulnerability on their device. For one, they can simply flash a custom ROM that’s not based on OnePlus’OxygenOS. A more experienced user could hex-edit the code in their bootloader and call for the exploit’s code to be changed upon execution, which would keep it from being noticed by the low-level Android system flag that triggers the change. They could also hide the code, or replace all references to SELinux in the OxygenOS code to something else so that the commands detailed above don’t trigger, though that could prove dicey for privileged operations like device updates.