Download latest Android KitKat 4.4.2 stock firmware for Cube U25GT tablet from here or from here. Download another Cube firmware from here.
Model: Cube U25GT tablet
Image file size: 304 MB
Platform: Mediatek MTK8127
Caution: Please do not update firmware unless you know what you are doing, you really want it or it is absolutely necessary. Firmware updates may occasionally have bad results, like bricking your device, temporarily or permanently. The firmware update process is done entirely at your own risk. Before attempting to update the firmware, back up your data.