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Cross-site Scripting occurrences in Cross Reference
An issue was discovered in the Cross Reference Add-on 36 for Google Docs. Stored XSS in the preview boxes in the configuration panel may allow a malicious user to use both label text and references text to inject arbitrary JavaScript code (via SCRIPT elements, event handlers, etc.). Since this code is stored by the plugin, the attacker may be able to target anyone who opens the configuration panel of the plugin. (2019-01-31, CVE-2019-7250)
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>