Stored Cross-Site Scripting (XSS) vulnerabilities occur when an attacker is able to inject malicious scripts into webpages that are later accessed by other users. In the case of the AI Feeds plugin for WordPress, the vulnerability arises from inadequate input sanitization and output escaping of user-provided data through the 'aife_post_meta' shortcode. An attacker with Contributor-level access or higher can exploit this flaw to inject arbitrary web scripts. These scripts are then executed in the context of any users who view the page, potentially leading to session hijacking, defacement, or redirection to malicious sites. This vulnerability is particularly concerning for sites that allow multiple contributors, as it lowers the bar for potential attackers to execute harmful scripts.

To mitigate this vulnerability, it is essential to apply input validation and output escaping properly. Use functions like `esc_html()` and `sanitize_text_field()` to sanitize user inputs and escape outputs in WordPress. Limiting the roles that can use specific shortcodes and reviewing permissions for contributor roles can also reduce risk.