A bug is currently in WebView on Android 4.3 and below and it is affecting 60 percent of all Android users. Google doesn't have plans to fix the bug, and that has caused some criticism of Google to come forth. The company will, at most, notify OEMs of the issue but since the bug is in devices running a version of Android below 4.4, it won't develop a patch by itself.
The bug is not affecting Android 4.4 or Android 5.0 since those versions use Blink instead of WebKit for the WebView component. Fragmentation with Android has left many users with old versions of Android, and they may not get any help from Google with this issue.
Interestingly enough, the Android team intends to continue fixing issues with other parts of old Android versions, just not WebView. Google has not released many details about the bug either, so people running Android 4.3 or below are out of luck as far as we can tell.