published April 25, 2019
The ASUS ZenFone 3 Max Android device with a build fingerprint of asus/US_Phone/ASUS_X008_1:7.0/NRD90M/US_Phone-14.14.1711.92-20171208:user/release-keys contains the android framework (i.e., system_server) with a package name of android (versionCode=24, versionName=7.0) that has been modified by ASUS or another entity in the supply chain. The system_server process in the core android package has an exported broadcast receiver that allows any app co-located on the device to programmatically initiate the taking of a screenshot and have the resulting screenshot be written to external storage (i.e., sdcard). The taking of a screenshot is not transparent to the user; the device has a screen animation as the screenshot is taken and there is a notification indicating that a screenshot occurred. If the attacking app also requests the EXPAND_STATUS_BAR permission, it can wake the device up using certain techniques and expand the status bar to take a screenshot of the user's notifications even if the device has an active screen lock. The notifications may contain sensitive data such as text messages used in two-factor authentication. The system_server process that provides this capability cannot be disabled, as it is part of the Android framework. The notification can be removed by a local Denial of Service (DoS) attack to reboot the device.