CVE-2018-18245 in Nagios
Summary
by MITRE
Nagios Core 4.4.2 has XSS via the alert summary reports of plugin results, as demonstrated by a SCRIPT element delivered by a modified check_load plugin to NRPE.
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Analysis
by VulDB Data Team • 06/19/2023
Nagios Core 4.4.2 contains a cross-site scripting vulnerability that arises from insufficient input validation and output encoding in the alert summary reports functionality. This vulnerability specifically affects the handling of plugin results within the web interface, where user-supplied data from external plugins is directly rendered without proper sanitization. The issue manifests when a modified check_load plugin delivers malicious SCRIPT elements through NRPE (Nagios Remote Plugin Executor), which are then executed in the context of authenticated users' browsers. This vulnerability falls under CWE-79, which defines cross-site scripting as a critical weakness in web applications where untrusted data is improperly incorporated into web pages.
The technical flaw stems from the web interface's failure to properly escape or filter special characters in plugin output before displaying them in HTML contexts. When the alert summary reports are generated, the system directly incorporates plugin results into HTML markup without applying appropriate HTML escaping or context-specific encoding. This allows attackers to inject malicious script code that executes in the browser of any user who views the affected report page. The vulnerability is particularly concerning because it requires minimal privileges to exploit, as the malicious payload can be injected through a modified plugin that operates within the legitimate NRPE framework.
The operational impact of this vulnerability extends beyond simple script execution, as it provides attackers with the ability to steal session cookies, perform unauthorized actions on behalf of authenticated users, and potentially escalate privileges within the Nagios environment. An attacker who can influence plugin output through NRPE access can create persistent XSS payloads that remain active until the affected reports are cleared or the web interface is restarted. This vulnerability is particularly dangerous in enterprise environments where Nagios is used for critical infrastructure monitoring, as it could lead to complete compromise of monitoring systems and exposure of sensitive operational data.
Security practitioners should implement multiple layers of defense to mitigate this vulnerability. Input validation and output encoding should be strengthened throughout the web interface to ensure all user-supplied data is properly sanitized before rendering. The Nagios installation should be updated to a patched version that addresses the XSS vulnerability, as this represents the most effective remediation approach. Additionally, network segmentation and access controls should be implemented to limit who can modify plugins or access NRPE endpoints, reducing the attack surface. This vulnerability aligns with ATT&CK technique T1059.007 for command and scripting interpreter, as it leverages script execution within the web interface context, and represents a classic privilege escalation vector through web application exploitation. Organizations should also consider implementing Content Security Policy headers to provide additional protection against XSS attacks, though this should not be relied upon as the sole mitigation measure.