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Cross-site Scripting occurrences in Acs Aem Commons
ACS Commons version 5.1.x (and earlier) suffers from a Reflected Cross-site Scripting (XSS) vulnerability in /apps/acs-commons/content/page-compare.html endpoint via the a and b GET parameters. User input submitted via these parameters is not validated or sanitised. An attacker must provide a link to someone with access to AEM Author, and could potentially exploit this vulnerability to inject malicious JavaScript content into vulnerable form fields and execute it within the context of the victim's browser. The exploitation of this issue requires user interaction in order to be successful. (2022-04-21, CVE-2022-28820)
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>