AI analysis
Paessler PRTG Network Monitor before version 26.2.120.1449 is affected by a reflected cross-site scripting flaw in its web interface. A request for a non-existent resource whose path ends in ".htm" returns an HTTP 403 "Forbidden Path" page that echoes the requested URL path into the HTML without proper output encoding. An unauthenticated remote attacker can trick a victim who already has an active PRTG session into opening a crafted link, causing arbitrary JavaScript to run in the security context of the PRTG web interface. Because the session cookie is not marked HttpOnly, that script can read and exfiltrate the cookie and may lead to session hijacking. No public proof-of-concept is known, and the issue is not listed in the CISA KEV catalog.
What to do: Upgrade Paessler PRTG Network Monitor to version 26.2.120.1449 or later. Until every instance is patched, restrict access to the PRTG web interface, warn operators not to open untrusted links while logged in, and invalidate active sessions if a user may have followed a suspicious link.
Affected
| Paessler PRTG Network Monitor | before 26.2.120.1449 |
Estimated exposure
moderatethousands to low tens of thousands of deployments — PRTG is a widely deployed commercial network-monitoring product; public internet scans have historically shown on the order of thousands of exposed web interfaces, with a larger number of internal-only installs, so the affected population…
Order-of-magnitude estimate by the model from install counts, market share and public scan data it knows; verify before quoting.
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.