The Photo Gallery, Sliders, Proofing and Themes – NextGEN Gallery plugin for WordPress is vulnerable to Stored DOM-Based Cross-Site Scripting via the 'comment' parameter in all versions up to, and including, 4.5.4 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. Exploitation requires the site to have Shutter or Shutter Reloaded selected as the active lightbox, and the injected comment must be approved through WordPress's standard moderation workflow before the payload is rendered to other visitors.