Download Stock Firmware for your Lenovo VIBE S850 Smartphone directly from official Lenovo servers. You can use this Stock ROM to flash or unbrick your Lenovo S850 Smartphone. Or you can unroot your device using this Stock ROM for Lenovo S850 smartphone.
Download and put this Lenovo S850 Stock ROM zip file at the root of your SD card. And then go to Recovery menu and apply updates from SD card. Click here for tutorial.
File name: S850_S926_VIBEUI_V2.0_1512_7.20.1_ST_S850_WC71.zip
File size: 723 MB