Newsletter Cross-site Scripting

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 (2022-06-20, CVE-2022-1889)

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. (2022-06-13, CVE-2022-1756)

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. (2021-01-01, CVE-2020-35933)

Cross site scripting is an attack where a web page executes code that is injected by an adversary. It usually appears, when users input is presented. This attack can be used to impersonate a user, take over control of the session, or even steal API keys.

The attack can be executed e.g. when you application injects the request parameter directly into the HTML code of the page returned to the user:

https://server.com/confirmation?message=Transaction+Complete

what results in:

<span>Confirmation: Transaction Complete</span>

In that case the message can be modified to become a valid Javascript code, e.g.:

https://server.com/confirmation?message=<script>dangerous javascript code here</script>

and it will be executed locally by the user's browser with full access to the user's personal application/browser data:

<span>Confirmation: <script>dangerous javascript code here</script></span>