Collapse-O-Matic < 1.8.5.6 - Authenticated (Contributor+) Stored Cross-Site Scripting via Shortcode

Description

The Collapse-O-Matic plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the plugin's 'expand' shortcode in all versions up to, and including, 1.8.5.5 due to insufficient input sanitization and output escaping on the 'tag' user supplied attribute. This makes it possible for authenticated attackers with contributor-level and above permissions to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.