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CVE-2026-4637

Reflected Cross-Site Scripting via URL Path in Paessler PRTG Network Monitor

CVSS 4.0 5.1 MEDIUMCheck source for fixed versionsKEV status unknown

Original advisory

cve-program · CVE-2026-4637

Published

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.

Read the publisher's advisory

Affected versions, risk and source history

cve-program · CVE-2026-4637

Published

PRTG Network Monitor

Vendor product

Publisher's version information

Shown as published. These rules are not interpreted as NuGet package version ranges.

{
                    "vendor": "Paessler GmbH",
                    "product": "PRTG Network Monitor",
                    "versions": [
                        {
                            "status": "affected",
                            "version": "0",
                            "lessThan": "26.2.120.1449",
                            "versionType": "custom"
                        }
                    ],
                    "defaultStatus": "unaffected"
                }

Original source record · Cite this exact observation · Complete original publisher JSON