---
id: CVE-2026-4637
title: >-
  Paessler PRTG Network Monitor before version 26.2.120.1449 is affected by a
  reflected Cross-Site Scripting (XSS) vulnerability
summary: >-
  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 …
severity: medium
cvss: 5.1
cvssVector: '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'
cwe:
  - CWE-79
vendor: Paessler GmbH
product: PRTG Network Monitor
affected:
  - prtg_network_monitor < 26.2.120.1449
published: '2026-09-24'
updated: '2026-09-24'
sourceUpdated: '2026-09-24T20:43:32.537'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-4637'
references:
  - url: 'https://paessler.freshdesk.com/en/support/solutions/articles/76000088640'
    label: 551230f0-3615-47bd-b7cc-93e92e730bbf
  - url: 'https://r.sec-consult.com/paessler'
    label: 551230f0-3615-47bd-b7cc-93e92e730bbf
  - url: 'https://www.paessler.com/de/download/'
    label: 551230f0-3615-47bd-b7cc-93e92e730bbf
  - url: 'https://www.paessler.com/prtg/prtg-network-monitor'
    label: 551230f0-3615-47bd-b7cc-93e92e730bbf
  - url: >-
      https://sec-consult.com/vulnerability-lab/advisory/multiple-vulnerabilities-in-paessler-prtg-network-monitor/
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
tags:
  - nvd
  - cve.org
  - exploit-available
exploitAvailable: true
ssvc:
  exploitation: poc
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-09-24T12:19:37.419469Z'
cvssSource: cna
ingestedAt: '2026-09-24T10:41:27.977Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.