Let us tell you beforehand that while this patch isn’t official one, but it’s reportedly based on official patch, and tricked up with slight modifications to make it work on all Android phones powered by MTK 6732 and 6752 MediaTek chips. You can then use the Stagefright Detector app to check out whether your device is affected y the said bug or not anymore.
Because it’s not official, you need TWRP recovery to install it on your device. Once you have the TWRP recovery, just download this small file (1.23 MB) from here, and flash it using the Install menu in TWRP recovery. Reboot system thereafter and your device would be fixed for Stagefright bug. Credit for making the flashable zip of the Stagefright fix goes to Miss Montage, thanks a lot! Update: it was originally developer by Dominic for jiayu.de.