The official WordPress Official Documentation (Codex) for these functions was not very clear and misled many plugin developers to use them in an insecure way. The developers assumed that these functions would escape the user input for them, when it does not. This simple detail, caused many of the most popular plugins to be vulnerable to XSS.

To date, this is the list of affected plugins:

Jetpack
WordPress SEO
Google Analytics by Yoast
All In one SEO
Gravity Forms
Multiple Plugins from Easy Digital Downloads
UpdraftPlus
WP-E-Commerce
WPTouch
Download Monitor
Related Posts for WordPress
My Calendar
P3 Profiler
Give
Multiple iThemes products including Builder and Exchange
Broken-Link-Checker
Ninja Forms

There are probably a few more that we have not listed. If you use WordPress, we highly recommend that you go to your wp-admin dashboard and update any out of date plugins now.