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Cross-site Scripting occurrences in Wp Subtitle
The WP Subtitle WordPress plugin before 3.4.1 adds a subtitle field and provides a shortcode to display it via [wp_subtitle]. The subtitle is stored as a custom post meta with the key: "wps_subtitle", which is sanitized upon post save/update, however is not sanitized when updating it directly from the post meta update button (via AJAX) - and this makes the XSS exploitable by authenticated users with a role as low as contributor. (2022-05-16, CVE-2022-1393)
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>