The Master Slider WordPress plugin through 3.11.2 does not sanitise and escape some of its shortcode attributes before outputting them in an inline script context, which could allow users with the Contributor role and above to perform Stored Cross-Site Scripting attacks that execute when the affected post is viewed.
No fixed version is available. Until one ships, restrict the Contributor role to trusted users, or deactivate the Master Slider WordPress plugin through 3.11.2. Site owners who need to keep it active can block the ms_slider shortcode for roles below Editor, for example with a shortcode-restriction Master Slider WordPress plugin through 3.11.2, which prevents the attack without removing the Master Slider WordPress plugin through 3.11.2.