Vulnerability Summary
Recently, I discovered a stored Cross-Site Scripting vulnerability in PRTG Network Monitor Version 21.1.66.1623+. The vulnerability exists in the email field of user details on the “User Accounts” page at /systemsetup.htm?tabid=5 when users are loaded from Active Directory. After the page loads, the email field is loaded with unescaped content, allowing malicious JavaScript to be reflected back to the user.
Proof of Concept and Exploitation Details
The vulnerability can be triggered by inserting HTML content, specifically script tags, into the email field of an Active Directory user. The following was inserted as a proof of concept to reflect the user’s cookie in an alert box:
<script>alert(document.cookie)</script>An example of this on one such user can be seen in the image below:
After loading the list of users, the HTML is then presented unescaped on the web page, which allows the script tags to be loaded as valid JavaScript. The unescaped HTML, as it loads in the browser, is seen in the next image:
Once the page loads, the JavaScript executes, displaying the user’s cookie to the screen, as shown in this picture:
Vulnerable Software Version
Raxis discovered this vulnerability on PRTG Network Monitor version 21.1.66.1623+.
Remediating the Vulnerability
Upgrade PRTG Network Monitor to Version 21.3.69.1333 or later immediately. The release notes and upgrade instructions can be found here: https://www.paessler.com/prtg/history/stable#21.3.69.1333.
Disclosure Timeline
- March 22, 2021 – Vulnerability reported to Paessler Technologies.
- March 25, 2021 – Vulnerability confirmed by Paessler Technologies.
- April 12, 2021 – CVE-2021-29643 assigned to this vulnerability.
- July 6, 2021 – Paessler releases version 21.3.69.1333 to address this vulnerability.
CVE Links & More
- Mitre CVE – https://cve.mitre.org/cgi-bin/cvename.cgi?name= CVE-2021-29643
- NVD – https://nvd.nist.gov/vuln/detail/CVE-2021-29643