A Reflected Authenticated Cross-Site Scripting (XSS) vulnerability in the Newsletter plugin before 6.8.2 for WordPress allows remote attackers to trick a victim into submitting a tnpc_render AJAX request containing either JavaScript in an options parameter, or a base64-encoded JSON string containing JavaScript in the encoded_options parameter.

The Newsletter WordPress plugin before 7.4.5 does not sanitize and escape the $_SERVER['REQUEST_URI'] before echoing it back in admin pages. Although this uses addslashes, and most modern browsers automatically URLEncode requests, this is still vulnerable to Reflected XSS in older browsers such as Internet Explorer 9 or below.

The Newsletter WordPress plugin before 7.4.6 does not escape and sanitise the preheader_text setting, which could allow high privilege users to perform Stored Cross-Site Scripting attacks when the unfilteredhtml is disallowed

Cross-site scripting vulnerability in Newsletter versions prior to 7.6.9 allows a remote unauthenticated attacker to inject an arbitrary script.

The Newsletter plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'newsletter_form' shortcode in versions up to, and including, 7.8.9 due to insufficient input sanitization and output escaping on user supplied attributes. This makes it possible for authenticated attackers with contributor-level and above permissions to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.

The Newsletter plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'np1' parameter in all versions up to, and including, 8.3.4 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.

The Newsletter WordPress plugin before 8.8.5 does not validate and escape some of its Widget options before outputting them back in a page/post where the block is embed, which could allow high privilege users such as admin to perform Stored Cross-Site Scripting attacks even when the unfiltered_html capability is disallowed (for example in multisite setup).

The Newsletter WordPress plugin before 8.85 does not sanitise and escape some of its Form settings, which could allow high privilege users such as admin to perform Stored Cross-Site Scripting attacks even when the unfiltered_html capability is disallowed (for example in multisite setup).

The Newsletter WordPress plugin before 8.7.1 does not sanitise and escape some of its settings, which could allow high privilege users such as admin to perform Stored Cross-Site Scripting attacks even when the unfiltered_html capability is disallowed (for example in multisite setup).

The Newsletter WordPress plugin before 8.8.2 does not sanitise and escape some of its Subscription settings, which could allow high privilege users such as admin to perform Stored Cross-Site Scripting attacks even when the unfiltered_html capability is disallowed (for example in multisite setup).