CVE-2020-10821 in Nagios XI
Summary
by MITRE
Nagios XI 5.6.11 allows XSS via the account/main.php theme parameter.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 05/11/2025
Nagios XI version 5.6.11 contains a cross-site scripting vulnerability in the account/main.php endpoint where the theme parameter is not properly sanitized, allowing attackers to inject malicious scripts into the web application. This vulnerability exists within the web interface of the network monitoring system, which is commonly deployed in enterprise environments for critical infrastructure monitoring and alerting. The affected parameter resides in the URL structure where users can specify their preferred interface theme, making this attack vector accessible through standard web browser interactions. The vulnerability is classified as a client-side attack that can compromise user sessions and potentially escalate to full system compromise when combined with other exploitation techniques. According to the CWE database, this represents a classic cross-site scripting flaw categorized under CWE-79, which specifically addresses improper neutralization of input during web page generation.
The technical exploitation of this vulnerability occurs when an attacker crafts a malicious URL containing script code within the theme parameter value. When a victim with valid credentials accesses this crafted URL, the malicious script executes in the victim's browser context within the Nagios XI application. This allows attackers to steal session cookies, perform unauthorized actions on behalf of users, or redirect victims to malicious websites. The vulnerability is particularly concerning in enterprise environments where Nagios XI is used for monitoring critical systems, as compromised user sessions could provide attackers with access to sensitive network monitoring data and system configurations. The attack requires no special privileges to initiate, making it accessible to any user with valid login credentials, and can be delivered through phishing emails, compromised websites, or social engineering campaigns.
The operational impact of this vulnerability extends beyond simple script execution as it can lead to complete compromise of the monitoring infrastructure. An attacker who successfully exploits this vulnerability can access all monitoring data, modify alert configurations, and potentially gain insights into network vulnerabilities that could be leveraged for further attacks. The compromised monitoring system may fail to detect malicious activities or provide false alerts, creating blind spots in the organization's security posture. Organizations using Nagios XI in production environments face significant risk of undetected intrusions, data exfiltration, and service disruption. The vulnerability affects the integrity and availability of the monitoring system, potentially leading to security incidents going unnoticed for extended periods. This aligns with ATT&CK technique T1566 which covers social engineering methods that can be used to deliver malicious payloads through web-based attacks.
Organizations should immediately apply the vendor-provided patch or upgrade to a version that addresses this vulnerability. The patch typically involves proper input sanitization and output encoding of the theme parameter to prevent script injection. System administrators should also implement additional security controls such as web application firewalls that can detect and block malicious script payloads in real-time. Regular security assessments should include testing for similar vulnerabilities in other web applications within the organization's attack surface. Network monitoring should be enhanced to detect unusual traffic patterns that may indicate exploitation attempts. Security awareness training should be provided to users to recognize phishing attempts that may deliver malicious URLs. The vulnerability demonstrates the importance of input validation and output encoding practices in web application development, as specified in OWASP Top 10 and secure coding standards. Organizations should also consider implementing additional access controls and monitoring for administrative functions within the Nagios XI interface to limit the potential impact of successful exploitation.