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Cross-site Scripting occurrences in Prism
Prism is a syntax highlighting library. Starting with version 1.14.0 and prior to version 1.27.0, Prism's command line plugin can be used by attackers to achieve a cross-site scripting attack. The command line plugin did not properly escape its output, leading to the input text being inserted into the DOM as HTML code. Server-side usage of Prism is not impacted. Websites that do not use the Command Line plugin are also not impacted. This bug has been fixed in v1.27.0. As a workaround, do not use the command line plugin on untrusted inputs, or sanitize all code blocks (remove all HTML code text) from all code blocks that use the command line plugin. (2022-02-18, CVE-2022-23647)
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>