CVE-2026-4637
Reflected Cross-Site Scripting via URL Path in Paessler PRTG Network Monitor
- State
- Published
- Severity
- 5.1 Medium
- Published
- Sep 24, 2026
- Updated
- Sep 24, 2026
- Reserved
- Mar 23, 2026
Description
Paessler PRTG Network Monitor before version 26.2.120.1449 is affected by a reflected Cross-Site Scripting (XSS) vulnerability. When a request is made for a non-existent resource ending in \".htm\", the web interface returns an HTTP 403 \"Forbidden Path\" error page that echoes the requested URL path into the HTML response body without proper output encoding or sanitization.
An unauthenticated, remote attacker can craft a URL containing an HTML/JavaScript payload in the path (e.g. https:////welcome.htm) and, once a victim with an active PRTG session opens the crafted link, execute arbitrary JavaScript in the security context of the PRTG web interface. Because the PRTG session cookie is not protected with the HttpOnly attribute, successful exploitation allows the attacker to read and exfiltrate the victim's session cookie, potentially leading to session hijacking.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 5.1 Medium | CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N | SEC-VLab |
Weaknesses
- CWE-79 Improper neutralization of input during web page generation ('cross-site scripting')
Affected Products
| Product | Versions |
|---|---|
PRTG Network MonitorPaessler GmbH |
|
References
- https://paessler.freshdesk.com/en/support/solutions/articles/76000088640vendor-advisory
- https://www.paessler.com/de/download/patch
- https://www.paessler.com/prtg/prtg-network-monitorproduct
- https://r.sec-consult.com/paesslerthird-party-advisory
- https://sec-consult.com/vulnerability-lab/advisory/multiple-vulnerabilities-in-paessler-prtg-network-monitor/exploit
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