CVE-2026-109357: LibreNMS LDAP filter injection in external authorization modes

CVE-2026-109357 · Severity: high · CVSS 8.1 · Published 2026-10-12

LibreNMS is a network monitoring platform that tracks devices and generates alerts. When configured with LDAP or Active Directory authorization, an unauthenticated attacker can inject wildcard characters into login requests to bypass authentication and gain full administrator access. This allows attackers to steal credentials for monitored devices, modify alert rules, create API tokens, and potentially execute arbitrary commands on the monitoring platform.

Technologies: Librenms. Vendors: Librenms.

Quick answers

Is CVE-2026-109357 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-109357 being exploited in the wild.
How severe is CVE-2026-109357?
High severity, with a CVSS score of 8.1, published 12 October 2026.
Which products and versions are affected?
Librenms before 26.9.0.
Is there a fix for CVE-2026-109357?
Yes: fixed in 26.9.0. Until then: Ensure the web server explicitly forwards the REMOTE_USER variable to PHP (e.g., via fastcgi_param REMOTE_USER $remote_user; in Nginx), which prevents the fallback to attacker-controlled PHP_AUTH_USER. Alternatively, disable ldap-authorization and ad-authorization modes until upgrading. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-109357 attacked?
It is attacked over the network, in a web application.
Am I affected by CVE-2026-109357?
Check whether you run Librenms at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • Fixed in: 26.9.0

Ensure the web server explicitly forwards the REMOTE_USER variable to PHP (e.g., via fastcgi_param REMOTE_USER $remote_user; in Nginx), which prevents the fallback to attacker-controlled PHP_AUTH_USER. Alternatively, disable ldap-authorization and ad-authorization modes until upgrading.

Technical details

The vulnerability is an LDAP filter injection (CWE-90) in the ldap-authorization and ad-authorization modes. Usernames from the HTTP Authorization header (PHP_AUTH_USER) are interpolated directly into LDAP search filters without escaping. Because these authorization modes perform only an existence check (no password bind), an attacker can inject wildcard characters (e.g., "*") to match all LDAP users and bypass authentication entirely, then match all group memberships to gain admin-level roles.

Affected products

  • LibreNMS LibreNMS before 26.9.0

Timeline

  • 2026-09-23: disclosed
  • 2026-10-12: advisory

References

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