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Cross-site Scripting occurrences in Gutenberg
The Gutenberg plugin through 13.7.3 for WordPress allows stored XSS by the Contributor role via an SVG document to the "Insert from URL" feature. NOTE: the XSS payload does not execute in the context of the WordPress instance's domain; however, analogous attempts by low-privileged users to reference SVG documents are blocked by some similar products, and this behavioral difference might have security relevance to some WordPress site administrators. (2022-07-30, CVE-2022-33994)
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>