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Cross-site Scripting occurrences in Wfilter Internet Content Filter
Wfilter ICF 5.0.117 contains a cross-site scripting (XSS) vulnerability. An attacker in the same LAN can craft a packet with a malicious User-Agent header to inject a payload in its logs, where an attacker can take over the system by through its plugin-running function. (2021-04-15, CVE-2021-3243)
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>