CVE-2026-45694: LibreNMS Cross-Site Scripting Vulnerability

MODERATE
Advisory Identifier: GHSA-jmqm-f8q4-v7wx
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CVSS 5.4
CWE-79
Published
Advisory Summary

CVE-2026-45694 is a MODERATE (CVSS 5.4) cross-site scripting vulnerability (CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')) affecting LibreNMS libraries in the Packagist ecosystem. The issue involves reflected xss via proxmox instance/vmid get parameters injected into document.title javascript assignment. Remediation is available by upgrading affected packages to version 26.5.0.

CVE-2026-45694 at a Glance

CVE Identifier CVE-2026-45694
GHSA Identifier GHSA-jmqm-f8q4-v7wx
Severity MODERATE
CVSS v3.1 Base Score 5.4
CWE Classification CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Affected Product LibreNMS
Package Ecosystem Packagist
Published Date
Last Updated

Security Impact

CVSS: 5.4

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required Low (PR:L)
User Interaction Required (UI:R)
Scope Changed (S:C)
Confidentiality Low (C:L)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2026-45694

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

librenms/librenms fixed: 26.5.0 
Upgrade librenms/librenms to 26.5.0
Verify Direct and Transitive Dependencies

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

inspect dependencies for librenms/librenms

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-45694, inspect your project dependencies for LibreNMS:

inspect dependencies for librenms/librenms

Analyze the terminal output to locate any version of LibreNMS in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 26.5.0), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

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 LibreNMS, 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

### Summary `LegacyController.php:75` writes the page title into a `document.title` JS assignment using string interpolation. `apps/proxmox.inc.php` pushes `$vars['instance']` and `$vars['vmid']` (GET params, only `strip_tags()` applied) directly into `$pagetitle`. A single quote terminates the JS string, executing arbitrary script. ### Details ```php // LegacyController.php:75 $html .= "<script>\ndocument.title = '$title';\n</script>"; // proxmox.inc.php:38,42 $pagetitle[] = $instance; // GET ?instance= $pagetitle[] = $vars['vmid']; // GET ?vmid= ``` ### PoC ``` http://target/apps?app=proxmox&instance=%27%3Balert%28document.cookie%29%3B// Confirmed in response: document.title = 'Apps - Proxmox - ';alert(document.cookie);// - LibreNMS'; ``` ### Fix ```php // LegacyController.php:75 $html .= "<script>\ndocument.title = " . json_encode($title) . ";\n</script>"; ``` Also wrap `$instance` and `$vars['vmid']` in `htmlspecialchars()` in proxmox.inc.php. ### Prerequisite Any authenticated session. Victim must follow a crafted link.

CVE-2026-45694 Affected LibreNMS Versions

1 component(s)
Fixed Versions:
26.5.0
Product / Package Ecosystem Affected Versions Fixed Version
librenms/librenms
 Packagist
< 26.5.0
26.5.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/librenms/librenms/security/advisories/GHSA-jmqm-f8q4-v7wx
LibreNMS Source Repository REPOSITORY
https://github.com/librenms/librenms
LibreNMS Release RELEASE
https://github.com/librenms/librenms/releases/tag/26.5.0

Frequently Asked Questions

What is CVE-2026-45694?
CVE-2026-45694 is a security vulnerability in LibreNMS involving Reflected XSS via Proxmox instance/vmid GET parameters injected into document.title JavaScript assignment under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting').
Which LibreNMS versions are affected?
Affected versions include releases prior to 26.5.0 across affected packages: librenms/librenms.
What version fixes CVE-2026-45694?
Upgrading to 26.5.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is librenms/librenms affected?
Yes, librenms/librenms is affected in releases prior to 26.5.0. Upgrade your dependency to 26.5.0 or later.
What is the CVSS score of CVE-2026-45694?
CVE-2026-45694 has a CVSS v3.1 base score of 5.4 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N.
What CWE is associated with CVE-2026-45694?
CVE-2026-45694 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 Packagist dependencies for CVE-2026-45694?
Run the dependency tree command: 'inspect dependencies for librenms/librenms'. 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-jmqm-f8q4-v7wx",
  "modified" : "2026-08-12T15:16:22Z",
  "published" : "2026-08-12T15:16:22Z",
  "aliases" : [ "CVE-2026-45694" ],
  "summary" : "LibreNMS: Reflected XSS via Proxmox instance/vmid GET parameters injected into document.title JavaScript assignment",
  "details" : "### Summary\n`LegacyController.php:75` writes the page title into a `document.title` JS assignment using string interpolation. `apps/proxmox.inc.php` pushes `$vars['instance']` and `$vars['vmid']` (GET params, only `strip_tags()` applied) directly into `$pagetitle`. A single quote terminates the JS string, executing arbitrary script.\n\n### Details\n```php\n// LegacyController.php:75\n$html .= \"<script>\\ndocument.title = '$title';\\n</script>\";\n\n// proxmox.inc.php:38,42\n$pagetitle[] = $instance;     // GET ?instance=\n$pagetitle[] = $vars['vmid']; // GET ?vmid=\n```\n\n### PoC\n```\nhttp://target/apps?app=proxmox&instance=%27%3Balert%28document.cookie%29%3B//\n\nConfirmed in response:\ndocument.title = 'Apps - Proxmox - ';alert(document.cookie);// - LibreNMS';\n```\n\n### Fix\n```php\n// LegacyController.php:75\n$html .= \"<script>\\ndocument.title = \" . json_encode($title) . \";\\n</script>\";\n```\nAlso wrap `$instance` and `$vars['vmid']` in `htmlspecialchars()` in proxmox.inc.php.\n\n### Prerequisite\nAny authenticated session. Victim must follow a crafted link.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "librenms/librenms"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "26.5.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 26.4.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/librenms/librenms/security/advisories/GHSA-jmqm-f8q4-v7wx"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/librenms/librenms"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/librenms/librenms/releases/tag/26.5.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-12T15:16:22Z",
    "nvd_published_at" : null
  }
}