---
cve: "CVE-2026-4637"
severity: "MEDIUM"
cvss: 5.1
epss: ""
vendor: "Paessler GmbH"
kev: false
exploited: false
published: "2026-09-24 10:05:06"
tags: [cve, security, medium]
source: tsecurity.de CVE-Dossier
exported: "2026-09-28T21:32:17+02:00"
---

# CVE-2026-4637

> 5.1 MEDIUM

## Beschreibung

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.

## CISA-Anreicherung (vulnrichment/ADP)

- CISA-SSVC (Coordinator, v2.0.3):
  - Exploitation: **poc**
  - Automatable: **yes**
  - Technical Impact: **partial**

## CVSS-Vektor

```
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
```

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Netzwerk | bad |
| AC Komplexität | Gering | bad |
| PR Privilegien | Keine | bad |

## BSI-Hinweise (deutsch)

- [Paessler PRTG: Mehrere Schwachstellen](https://wid.cert-bund.de/portal/wid/sicherheitshinweis/WID-SEC-W-2026-3565) — _BSI-Einstufung: hoch_
  Ein Angreifer kann mehrere Schwachstellen in Paessler PRTG ausnutzen, um Cross-Site-Scripting-Angriffe durchzuführen, Sicherheitsmaßnahmen zu umgehen und vertrauliche Informationen offenzulegen.

## Referenzen

- <https://paessler.freshdesk.com/en/support/solutions/articles/76000088640>
- <https://www.paessler.com/de/download/>
- <https://www.paessler.com/prtg/prtg-network-monitor>
- <https://r.sec-consult.com/paessler>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-4637) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI WID (CSAF)_