The Newsletters WordPress plugin before 4.17 does not perform any nonce or capability check when saving one of its settings screens, and writes every submitted parameter into its own options, allowing attackers to make a logged in administrator overwrite arbitrary Newsletters WordPress plugin before 4.17 settings, including the credential protecting its API, via a Cross-Site Request Forgery attack.

The Newsletters WordPress plugin before 4.16 does not strictly compare its API authentication key, allowing unauthenticated attackers to bypass the API authentication via type juggling and perform privileged actions such as modifying subscriber records and sending emails, when the optional API has been enabled.

The Newsletters plugin for WordPress is vulnerable to time-based SQL Injection via the ‘orderby' parameter in all versions up to, and including, 4.9.9.8 due to insufficient escaping on the user supplied parameter and lack of sufficient preparation on the existing SQL query. This makes it possible for authenticated attackers, with Contributor-level access and above, to append additional SQL queries into already existing queries that can be used to extract sensitive information from the database.

The Newsletters plugin for WordPress is vulnerable to Reflected Cross-Site Scripting via the "to" parameter in all versions up to, and including, 4.9.9.7 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that execute if they can successfully trick an admin user into performing an action such as clicking on a link.

The Newsletters plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the plugin's newslettersvideo shortcode in all versions up to, and including, 4.9.9.4 due to insufficient input sanitization and output escaping on user supplied attributes. This makes it possible for authenticated attackers, with contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.

The Newsletters plugin for WordPress is vulnerable to Full Path Disclosure in all versions up to, and including, 4.9.9. This is due the plugin not preventing direct access to the /vendor/mobiledetect/mobiledetectlib/export/exportToJSON.php. This makes it possible for unauthenticated attackers to retrieve the full path of the web application, which can be used to aid other attacks. The information displayed is not useful on its own, and requires another vulnerability to be present for damage to an affected website.