The Vivo V7 device with a build fingerprint of…

Summary

The Vivo V7 device with a build fingerprint of vivo/1718/1718:7.1.2/N2G47H/compil11021857:user/release-keys allows any app co-located on the device to set system properties as the com.android.phone user. The com.qualcomm.qti.modemtestmode app (versionCode=25, versionName=7.1.2) that contains an exported service named com.qualcomm.qti.modemtestmode.MbnTestService that allows any app co-located on the device to provide key-value pairs to set certain system properties. Notably, system properties with the persist.* prefix can be set which will survive a reboot. On the Vivo V7 device, when the persist.sys.input.log property is set to have a value of yes, the user's screen touches be written to the logcat log by the InputDispatcher for all apps. The system-wide logcat log can be obtained from external storage via a different known vulnerability on the device. The READ_EXTERNAL_STORAGE permission is necessary to access the log files containing the user's touch coordinates. With some effort, the user's touch coordinates can be mapped to key presses on a keyboard.