Reflected Cross-Site Scripting via URL Path in Paessler PRTG Network Monitor (CVE-2026-4637) | HOL Guard CVE

Medium · CVSS 5.1CVE-2026-4637

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

Answer in brief

CVE-2026-4637 records a Medium severity (CVSS 5.1) vulnerability in Reflected Cross-Site Scripting via URL Path in Paessler PRTG Network Monitor. The current sources do not mark it as known exploited. The current feed maps Paessler GmbH/PRTG Network Monitor (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 24, 2026Updated Sep 24, 2026Source checked Sep 24, 2026First seen by HOL Sep 24, 2026Material review Sep 24, 2026

Upstream Advisory

Key facts

Risk: Medium · CVSS 5.1
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

CVSS is 5.1. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Paessler GmbH/PRTG Network Monitor (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Paessler GmbH/PRTG Network Monitorgeneric	>=0 <26.2.120.1449	26.2.120.1449

Recommended response

Check inventory. Check lockfiles and deployed manifests for Paessler GmbH/PRTG Network Monitor.
Review the reported fix. Update Paessler GmbH/PRTG Network Monitor to 26.2.120.1449 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 24, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 24, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 24, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.