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Cross-site Scripting occurrences in Dart Software Development Kit
Bad validation logic in the Dart SDK versions prior to 2.12.3 allow an attacker to use an XSS attack via DOM clobbering. The validation logic in dart:html for creating DOM nodes from text did not sanitize properly when it came across template tags. (2021-04-22, CVE-2021-22540)
An improper HTML sanitization in Dart versions up to and including 2.7.1 and dev versions 2.8.0-dev.16.0, allows an attacker leveraging DOM Clobbering techniques to skip the sanitization and inject custom html/javascript (XSS). Mitigation: update your Dart SDK to 2.7.2, and 2.8.0-dev.17.0 for the dev version. If you cannot update, we recommend you review the way you use the affected APIs, and pay special attention to cases where user-provided data is used to populate DOM nodes. Consider using Element.innerText or Node.text to populate DOM elements. (2020-03-26, CVE-2020-8923)
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>