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Cross-site Scripting occurrences in Web Isolation
Symantec Web Isolation (WI) 1.11 prior to 1.11.21 is susceptible to a reflected cross-site scripting (XSS) vulnerability. A remote attacker can target end users protected by WI with social engineering attacks using crafted URLs for legitimate web sites. A successful attack allows injecting malicious JavaScript code into the website's rendered copy running inside the end user's web browser. It does not allow injecting code into the real (isolated) copy of the website running on the WI Threat Isolation Engine. (2018-10-22, CVE-2018-12246)
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>