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Cross-site Scripting occurrences in Wp Html Author Bio
The WP HTML Author Bio WordPress plugin through 1.2.0 does not sanitise the HTML allowed in the Bio of users, allowing them to use malicious JavaScript code, which will be executed when anyone visit a post in the frontend made by such user. As a result, user with a role as low as author could perform Cross-Site Scripting attacks against users, which could potentially lead to privilege escalation when an admin view the related post/s. (2021-10-11, CVE-2021-24545)
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>