Well, this is pretty horrible. Google is refusing to fix a bug in Android older than version 4.3, shifting the responsibility back to the discoverer of the bug, or the manufacturer of the device (Samsung, Motorola, etc) - even if it appears to be a critical security vulnerability, as with the latest one in the WebView browser rendering engine.
ExtremeTechThe flaws in this case affect Android 4.1 to 4.3, aka Jelly Bean, which began shipping in mid-2012 and was the primary version of Android through late 2013, or roughly 14 months ago. Up until quite recently, Google has aggressively patched problems in Android’s WebView rendering engine. Before KitKat (Android 4.4), all versions of Android used the version of WebView found within the Android Browser for rendering HTML webpages. With KitKat and Lollipop, Google updated the operating system to use a WebView plugin derived from its Chromium project
The average phone or tablet buyer has no way to upgrade their operating system unless the carrier provides an OTA update, and two-year upgrade cycles means that plenty of people are going to be stuck on broken devices with known exploits that Google isn’t going to fix. Granted, the fact that Google fixes an exploit doesn’t mean that carriers will deploy it, and fragmentation has been a major problem in Android’s ecosystem over the years — but there’s a difference between acknowledging the difficulty of maintaining security updates for the entirety of one’s user base and flatly refusing to do them.