LibreNMS: Reflected XSS via Proxmox instance/vmid GET parameters injected into document.title JavaScript assignment
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
// 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
// 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.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Composer package | librenms/librenms | < 26.5.0 | 26.5.0 |
References
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N- Weakness (CWE)
CWE-79- Platform
- Composer
- Package
librenms/librenms- Disclosed
- 12.08.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-jmqm-f8q4-v7wx - CC BY 4.0
Vulnerability history: librenms/librenms
All published vulnerabilities of this package (Composer package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 106
- First → latest
- 10.2019 08.2026
- Without a fix
- 6
- Exploited in attacks
- 0
Severity breakdown
- Critical 5
- High 39
- Medium 56
- Low 6
Disclosures per year
- 2019: 6
- 2020: 0
- 2021: 7
- 2022: 26
- 2023: 12
- 2024: 24
- 2025: 15
- 2026: 16
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LibreNMS: Reflected XSS via Proxmox instance/vmid GET parameters injected into document.title JavaScript assignment this entry
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