CVE-2023-53690 is a stored cross-site scripting (XSS) vulnerability classified under CWE-79 affecting Nagios Fusion versions prior to 4.2.0. The flaw exists in the LDAP/AD authentication-server configuration interface, where user input is not properly sanitized before being stored and subsequently rendered in the administrative user interface. This improper neutralization of input allows an attacker with the ability to add or modify authentication servers via LDAP/AD integration to inject malicious JavaScript payloads. When other administrators or users with access to the affected UI page view the stored data, the malicious script executes in their browser context. This can lead to session hijacking, theft of credentials, or unauthorized actions performed on behalf of the victim user. The vulnerability requires the attacker to have privileges to add authentication servers, which is a high privilege level, but does not require user interaction beyond viewing the affected page. The CVSS 4.0 vector indicates network attack vector, low attack complexity, no privileges required to exploit (though the description suggests high privileges are needed to add servers), and user interaction is required (viewing the page). The scope is high, as the vulnerability affects the administrative interface and can impact multiple users. No public exploits or active exploitation have been reported to date. Mitigation primarily involves upgrading to Nagios Fusion 4.2.0 or later where the issue is fixed, or applying strict input validation and output encoding on the affected fields. Monitoring administrative activities and restricting access to the LDAP/AD configuration interface can reduce risk. Given Nagios Fusion’s role in critical infrastructure monitoring, exploitation could have significant operational impacts.

For European organizations, the impact of CVE-2023-53690 can be significant due to Nagios Fusion’s widespread use in monitoring IT infrastructure and network health. Successful exploitation could allow attackers to execute arbitrary JavaScript in the context of administrative users, potentially leading to session hijacking, theft of sensitive credentials, or unauthorized changes to monitoring configurations. This could disrupt monitoring capabilities, delay incident detection, or provide a foothold for further internal compromise. Confidentiality and integrity of monitoring data and administrative controls are at risk. Availability impact is indirect but possible if attackers manipulate monitoring configurations or disable alerts. Given the administrative nature of the affected interface, the threat is particularly relevant to organizations with complex LDAP/AD integrations and multiple administrators. European critical infrastructure sectors such as finance, energy, telecommunications, and government agencies that rely on Nagios Fusion for operational monitoring are especially vulnerable. The medium CVSS score reflects moderate exploitability but significant potential impact on confidentiality and integrity.

1. Upgrade Nagios Fusion to version 4.2.0 or later where this vulnerability is patched. 2. If immediate upgrade is not possible, restrict access to the LDAP/AD authentication-server configuration interface to a minimal set of trusted administrators. 3. Implement strict input validation and output encoding on all user inputs related to authentication server configuration to prevent injection of malicious scripts. 4. Monitor administrative logs for unusual additions or modifications of authentication servers. 5. Educate administrators about the risks of stored XSS and encourage cautious review of configuration changes. 6. Employ Content Security Policy (CSP) headers to limit the impact of potential XSS payloads in the administrative UI. 7. Regularly audit Nagios Fusion deployments for outdated versions and apply security patches promptly. 8. Consider network segmentation to isolate monitoring infrastructure from general user networks to reduce exposure.