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Cross-site Scripting occurrences in Related Posts
The Related Posts for WordPress plugin through 2.0.4 does not sanitise its heading_text and CSS settings, allowing high privilege users (admin) to set XSS payloads in them, leading to Stored Cross-Site Scripting issues. (2021-07-19, CVE-2021-24482)
Unvalidated input and lack of output encoding within the Related Posts for WordPress plugin before 2.0.4 lead to a Reflected Cross-Site Scripting (XSS) vulnerability within the 'lang' GET parameter while editing a post, triggered when users with the capability of editing posts access a malicious URL. (2021-04-05, CVE-2021-24180)
Why Cross-site Scripting can be dangerous
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>