The Stackable – Page Builder Gutenberg Blocks plugin for WordPress has a security issue where attackers can insert their own harmful code into pages. This can happen if the attacker has Contributor-level access or higher. The plugin is vulnerable in all versions up to 3.13.1 because it does not properly filter and protect the data that is entered. This means that whenever a user views a page with the injected code, it will automatically run and potentially cause harm.