Better understanding and mitigating the risks of using a phone that no longer receives system updates
Too many perfectly usable phones are put into a questionable security situation by lack of vendor support for keeping key software up to date.
But what's the actual risk of using an Android phone on a stock ROM without updates? What's the attack surface?
It seems like most things that'd contact potentially malicious software are web and messaging software, but that's all done by apps which continue to receive updates (at least until the android version is entirely unsupported) eg. Webview, Firefox, Signal, etc.
So are the main avenues for attack then sketchy apps and wifi points? If one is careful to use a minimal set of widely scrutinised apps and avoid connecting to wifi/bluetooth/etc. devices of questionable provenance is it really taking that much of a risk to continue using a device past EOL?
Or do browsers rely on system libraries that have plausible attack vectors? Perhaps images, video, font etc. rendering could be compromised? At this point though, that stack must be quite hardened and mature, it'd be major news for libjpg/ffmpeg to have a code-execution vulnerability? Plus it seems unlikely that they wouldn't just include this in webview/Firefox as there must surely be millions of devices in this situation so why not take the easy step of distributing a bit more in the APK?
I'm not at all an Android developer though, perhaps this is very naive and I'm missing something major?
To be fair, unless you're using some incredibly obscure phone, chances are a ROM exists to keep it up to date long after the manufacturer has walked away from it.
I realize not everyone has the know how to install one, but if they're concerned, it's not hard to find someone who does. (we've all got techie friends, and if you don't, that means it's YOU).
Heck, my pixel 2XL was updated to the newest Android version up to last year thanks to the Pixel Experience ROM. Would likely still be updated if I hadn't finally upgraded.
You can update your phone with custom ROMs, but it won't update the closed source components of it(device drivers, bootloader, etc...). If a vulnerability is found in one of those components, it's unlikely that it will get parched
The vast majority of Android phones in the USA are locked. It has been impossible to upgrade the ROM on any flagship Galaxy for the better part of a decade here, and the few times it is possible, it'll also trip Knox and disable important features permanently.