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Cross-site Scripting occurrences in Slickquiz
An XSS issue was discovered in the slickquiz plugin through 1.3.7.1 for WordPress. The save_quiz_score functionality available via the /wp-admin/admin-ajax.php endpoint allows unauthenticated users to submit quiz solutions/answers, which are stored in the database and later shown in the WordPress backend for all users with at least Subscriber rights. Because the plugin does not properly validate and sanitize this data, a malicious payload in either the name or email field is executed directly within the backend at /wp-admin/admin.php?page=slickquiz across all users with the privileges of at least Subscriber. (2019-09-13, CVE-2019-12517)
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>