Input validation vulnerability in Photospace Responsive Gallery 2.1.1

The Photospace Responsive plugin for WordPress is vulnerable to a security issue called Stored Cross-Site Scripting. This issue allows attackers with administrator-level permissions to inject malicious code into pages on the website. This malicious code will then run whenever someone visits the injected page. This security issue only affects websites that have a multi-site installation or have disabled a security feature called unfiltered_html. Versions of the plugin up to and including 2.1.1 are affected.