Cloud Application Policy Infrastructure Controller Cross-site Scripting

A vulnerability in the web UI of Cisco Application Policy Infrastructure Controller (APIC) or Cisco Cloud APIC could allow an authenticated, remote attacker to perform a stored cross-site scripting attack on an affected system. This vulnerability is due to improper input validation in the web UI. An authenticated attacker could exploit this vulnerability by sending malicious input to the web UI. A successful exploit could allow the attacker to execute arbitrary script code in the context of the web-based interface or access sensitive, browser-based information. (2021-08-25, CVE-2021-1582)

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>