The WordPress Crelly Slider plugin, which has 20,000+ active installations, was prone to an authenticated arbitrary file upload vulnerability in version 1.3.4 and below.
The WordPress User Submitted Posts plugin (30,000+ active installations) was prone to an arbitrary file upload vulnerability in version 20190426 and below.
We are seeing today a lot of hacked WordPress blogs due to a critical vulnerability in the WordPress YellowPencil Visual CSS Style Editor plugin which has 30,000+ active installations.
Hackers are currently actively exploiting a vulnerability in the WordPress Related Posts plugin, which has 60,000+ active installations.
Starting from version 3.8.3, NinjaFirewall (WP and WP+ Edition) will attach a PHP backtrace to some important email notifications sent to the administrator.