Now that we've covered general and server security, let's deal with some security issues that are specific to mobile devices and Cordova apps.
Although your marketing department will cringe to hear me say this, targeting only modern devices is extremely important in order to maintain security. Older mobile devices (such as Android 2.x or lower) have several security vulnerabilities that will never be patched. In short, avoid them completely even if they still form a big part of the market.
I would highly suggest avoiding any device running a version of Android less than 4.x version. Cordova doesn't support Android version 3.x (Honeycomb), and version 2.x has too many issues to be secure. iOS users, on the other hand, often get security updates for their devices for two years and sometimes longer. Even so, I wouldn't support devices running iOS 5 or lower.