A prototype pollution vulnerability exists in Strikingly CMS which can result in reflected cross-site scripting (XSS) in affected applications and sites built with Strikingly. The vulnerability exists because of Strikingly JavaScript library parsing the URL fragment allows access to the __proto__ or constructor properties and the Object prototype. By leveraging an embedded gadget like jQuery, an attacker who convinces a victim to visit a specially crafted link could achieve arbitrary javascript execution in the context of the user\'s browser.