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Cross-site Scripting occurrences in Mystickymenu
The Floating Notification Bar, Sticky Menu on Scroll, and Sticky Header for Any Theme – myStickymenu WordPress plugin before 2.5.2 does not sanitise or escape its Bar Text settings, allowing hight privilege users to use malicious JavaScript in it, leading to a Stored Cross-Site Scripting issue, which will be triggered in the plugin's setting, as well as all front-page of the blog (when the Welcome bar is active) (2021-08-02, CVE-2021-24425)
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>