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Cross-site Scripting occurrences in Teler
teler is an real-time intrusion detection and threat alert dashboard. teler prior to version 2.0.0-rc.4 is vulnerable to DOM-based cross-site scripting (XSS) in the teler dashboard. When teler requests messages from the event stream on the `/events` endpoint, the log data displayed on the dashboard are not sanitized. This only affects authenticated users and can only be exploited based on detected threats if the log contains a DOM scripting payload. This vulnerability has been fixed on version `v2.0.0-rc.4`. Users are advised to upgrade. There are no known workarounds for this vulnerability. (2022-12-06, CVE-2022-23466)
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>