CVE-2026-4637: Software Security Vulnerability Vulnerability

MODERATE
Advisory Identifier: GHSA-xp6x-3pcm-f3ph
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CWE-79
Published
Advisory Summary

CVE-2026-4637 is a MODERATE security vulnerability vulnerability (CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')) affecting Software libraries in the Maven ecosystem. The weakness occurs when the product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.. Remediation is available in the latest vendor maintenance releases.

CVE-2026-4637 at a Glance

CVE Identifier CVE-2026-4637
GHSA Identifier GHSA-xp6x-3pcm-f3ph
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Affected Product Software
Package Ecosystem Maven
Published Date
Last Updated

How to Fix CVE-2026-4637

To remediate this vulnerability, upgrade all affected Software dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

mvn dependency:tree

How to Check if You Are Affected

To determine whether your Java application is affected by CVE-2026-4637, inspect your build dependencies using the Maven Dependency Plugin:

mvn dependency:tree

Analyze the terminal output to locate any version of Software in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than the patched release), your application is affected.

Note: The mvn dependency:tree command inspects the resolved dependency graph declared in your project's POM files; it does not perform automated security scanning or inspect runtime dynamic classpaths. Always verify runtime container classpaths and shaded JARs.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'), where the product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. In Software, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

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.

References

NVD — CVE-2026-4637 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-4637
paessler.freshdesk.com/en/support/solution... WEB
https://paessler.freshdesk.com/en/support/solutions/articles/76000088640
r.sec-consult.com/paessler WEB
https://r.sec-consult.com/paessler
sec-consult.com/vulnerability-lab/a... WEB
https://sec-consult.com/vulnerability-lab/advisory/multiple-vulnerabilities-in-paessler-prtg-network-monitor
www.paessler.com/de/download WEB
https://www.paessler.com/de/download
www.paessler.com/prtg/prtg-network-m... WEB
https://www.paessler.com/prtg/prtg-network-monitor

Frequently Asked Questions

What is CVE-2026-4637?
CVE-2026-4637 is a security vulnerability in Software classified as a security vulnerability vulnerability under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting').
Which Software versions are affected?
Affected versions include releases prior to current release patches.
What version fixes CVE-2026-4637?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
What CWE is associated with CVE-2026-4637?
CVE-2026-4637 is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.).
How can I check Maven dependencies for CVE-2026-4637?
Run the dependency tree command: 'mvn dependency:tree'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-xp6x-3pcm-f3ph",
  "modified" : "2026-09-24T15:31:29Z",
  "published" : "2026-09-24T12:31:23Z",
  "aliases" : [ "CVE-2026-4637" ],
  "details" : "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.\n\n\n\n\nAn 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.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X"
  } ],
  "affected" : [ ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-4637"
  }, {
    "type" : "WEB",
    "url" : "https://paessler.freshdesk.com/en/support/solutions/articles/76000088640"
  }, {
    "type" : "WEB",
    "url" : "https://r.sec-consult.com/paessler"
  }, {
    "type" : "WEB",
    "url" : "https://sec-consult.com/vulnerability-lab/advisory/multiple-vulnerabilities-in-paessler-prtg-network-monitor"
  }, {
    "type" : "WEB",
    "url" : "https://www.paessler.com/de/download"
  }, {
    "type" : "WEB",
    "url" : "https://www.paessler.com/prtg/prtg-network-monitor"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : false,
    "github_reviewed_at" : null,
    "nvd_published_at" : "2026-09-24T10:17:37Z"
  }
}