Ios Cross-site Scripting

A vulnerability in the web framework code of Cisco IOS and Cisco IOS XE Software could allow an authenticated, remote attacker to conduct a stored cross-site scripting (XSS) attack against a user of the web interface of the affected software using the banner parameter. The vulnerability is due to insufficient input validation of the banner parameters that are passed to the web server of the affected software. An attacker could exploit this vulnerability by crafting a banner parameter and saving it. The attacker could then convince a user of the web interface to access a malicious link or could intercept a user request for the affected web interface and inject malicious code into the request. A successful exploit could allow the attacker to execute arbitrary script code in the context of the affected web interface or allow the attacker to access sensitive browser-based information. (2019-09-25, CVE-2019-12668)

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>