HTB23176: Cross-Site Scripting (XSS) in GuppY

High-Tech Bridge Security Research Lab discovered two XSS vulnerabilities in GuppY, which can be exploited to perform Cross-Site Scripting attacks against users of vulnerable application.

Cross-Site Scripting (XSS) in GuppY vulnerability exists due to insufficient sanitisation of user-supplied data in "an" HTTP GET parameter passed to "/agenda.php" script. A remote attacker can trick a logged-in user to open a specially crafted link and execute arbitrary HTML and script code in browser in context of the vulnerable website.

The exploitation example below uses the "alert()" JavaScript function to display user's cookies:
http://[host]/agenda.php?agv=2&an=%22%20onmouseover%3dalert%28%27document.cookie%27%29%20%22

The second XSS vulnerability exists due to insufficient sanitisation of user-supplied data in "cat" HTTP GET parameter passed to "/mobile/thread.php" script. A remote attacker can trick a logged-in user to open a specially crafted link and execute arbitrary HTML and script code in browser in context of the vulnerable website.

The exploitation example below uses the "alert()" JavaScript function to display user's cookies:
http://[host]/mobile/thread.php?cat=1%22%20onmouseover%3dalert%28%27document.cookie%27%29%20%22

Solution: Update to GuppY 4.6.28

Source: High-Tech Bridge security advisory HTB23176.