The Newsletters WordPress plugin before 4.16 does not restrict the classes allowed when unserialising a value taken from a public form submission, allowing unauthenticated attackers to inject arbitrary PHP objects.

The Newsletters WordPress plugin before 4.15 does not prevent deserialization of untrusted input that is stored through a public form, allowing unauthenticated attackers to inject a PHP object and, via a property-oriented gadget chain bundled with the Newsletters WordPress plugin before 4.15, write arbitrary files and execute code on the server.

Unauthenticated Broken Access Control in Newsletters <= 4.13 versions.

The Newsletters plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the logging functionality 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 will execute whenever a user accesses an injected page.

Improper Neutralization of Input During Web Page Generation (XSS or 'Cross-site Scripting') vulnerability in Tribulant Newsletters allows Reflected XSS.This issue affects Newsletters: from n/a through 4.9.8.

The Newsletters plugin for WordPress is vulnerable to Local File Inclusion in all versions up to, and including, 4.9.9.9 via the 'file' parameter. This makes it possible for authenticated attackers, with Administrator-level access and above, to include and execute arbitrary files on the server, allowing the execution of any PHP code in those files. This can be used to bypass access controls, obtain sensitive data, or achieve code execution in cases where images and other “safe” file types can be uploaded and included.