Android 4.4.4 KitKat Stagefright vulnerability: Do-It-Yourself fix possible?

[lunta]

You all must be aware of the serious Stagefright-library vulnerability in almost all older Android versions found already last summer. I'm in a really bad position since Samsung won't update my Galaxy Ace 4/Style LTE (SM-G357FZ) phone anymore, nor do there exist any custom roms (e.g. CyanogenMod) that would fix it. Actually, there is a really little amount of information about hacking my phone online.

I'm reluctant to trash a perfectly good phone I bought a year ago, but do I have any changes to patch the Android myself? I found some firmware files for my phone online: Firmware for Samsung SM-G357FZ - SamMobile
I guess I could try to install bug-fixed StageFright-libraries into that firmware and flash it into my device, right? Unfortunately I have no experience in modifying Android. How could I apply the fix into the firmware files?

The downloaded firmware file contains the following files:

aboot.mbn
boot.img
cache.img.ext4
hidden.img.ext4
hyp.mbn
modem.bin
NON-HLOS.bin
recovery.img
rpm.mbn
sbl1.mbn
sec.dat
system.img.ext4
tz.mbn