Linksys WRT54G XSS Vulnerability

Description of Vulnerability:

Linksys WRT54G is a consumer wireless G broadband router and four port switch (http://www.linksysbycisco.com/ANZ/en/support/WRT54G). The device provides an administration interface for configuration via a web browser. Unfortunately the interface does not sanitize keywords for safe browsing leading to a stored/persistent cross site scripting (XSS) vulnerability.

Systems affected:

Cisco Linksys Wireless G Boradband Router WRT54G with firmware version 4.21.1 was tested and found to be vulnerable.

Proof of Concept:

1. Log into the WRT54G administration screen and navigate to /Filters.asp
2. Enter "' onBlur='alert("xss")" for the "Website Blocking by Keyword" value.
3. Click the 'Save Settings' button at the bottom of the form, ignore the error and click 'Continue'
4. After the page refreshes click on the "Website Blocking by Keyword" textfield then click outside to view the JavaScript alert