Vulnerability · Published Sep 24, 2026 · Assigned by SEC-VLab
CVE-2026-4637Reflected Cross-Site Scripting via URL Path in Paessler PRTG Network Monitor
Medium 5.1
In plain English
A medium-severity cross-site scripting in PRTG Network Monitor from Paessler GmbH. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 49% of all known vulnerabilities).
Official 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.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Paessler GmbH | PRTG Network Monitor | 0 – before 26.2.120.1449 |
Weakness: CWE-79 · Vector: 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
References
- https://paessler.freshdesk.com/en/support/solutions/articles/76000088640 vendor-advisory
- https://www.paessler.com/de/download/ patch
- https://www.paessler.com/prtg/prtg-network-monitor product
- https://r.sec-consult.com/paessler third-party-advisory
- https://sec-consult.com/vulnerability-lab/advisory/multiple-vulnerabilities-in-paessler-prtg-network-monitor/ exploit