CVE-2020-15903 in Nagios XI
Summary
by MITRE
An issue was found in Nagios XI before 5.7.3. There is a privilege escalation vulnerability in backend scripts that ran as root where some included files were editable by nagios user. This issue was fixed in version 5.7.3.
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Analysis
by VulDB Data Team • 09/10/2020
The vulnerability identified as CVE-2020-15903 represents a critical privilege escalation flaw within Nagios XI versions prior to 5.7.3, demonstrating a fundamental weakness in the software's access control mechanisms. This vulnerability resides in the backend script execution environment where certain critical components operate with root privileges while other elements remain accessible to the standard nagios user account. The flaw creates a dangerous condition where an attacker with access to the nagios user account can manipulate specific include files that are loaded by root-executed scripts, effectively enabling unauthorized code execution with elevated privileges. This type of vulnerability falls under the category of improper privilege handling as classified by CWE-276, where insufficient access control allows unauthorized users to gain elevated system privileges.
The technical exploitation of this vulnerability occurs through a classic file inclusion attack vector where the nagios user, who typically operates with limited privileges, can modify files that are subsequently included by backend processes running as root. When these scripts execute, they incorporate the modified files, allowing the attacker to inject malicious code that executes with root privileges. The backend scripts in question are designed to run with elevated permissions to perform system monitoring tasks, but the inclusion of user-editable files creates an attack surface that directly undermines the principle of least privilege. This issue aligns with ATT&CK technique T1068, which describes the exploitation of legitimate credentials and privileges to gain elevated access, and specifically targets the privilege escalation domain under ATT&CK tactic TA0004. The vulnerability represents a clear violation of the principle that processes should run with the minimum necessary privileges, as the root-privileged scripts directly include files that should remain protected from user modification.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it allows attackers to gain complete system control over the Nagios XI server. Once escalated to root privileges, an attacker can modify system configurations, install backdoors, exfiltrate sensitive monitoring data, or even compromise other systems within the network that the Nagios server monitors. The affected Nagios XI installations become potential entry points for broader network attacks, as the monitoring infrastructure often has access to critical network segments and system information. Organizations relying on Nagios XI for system monitoring face significant risk of data breaches, system compromise, and potential lateral movement within their networks. The vulnerability's exploitation requires only basic user-level access to the Nagios service, making it particularly dangerous as it can be exploited by attackers who gain access through other means such as credential theft or web application attacks against the Nagios web interface.
Mitigation strategies for CVE-2020-15903 require immediate implementation of the vendor-recommended update to Nagios XI version 5.7.3, which addresses the root cause by ensuring that include files are not editable by the nagios user account. Organizations should also implement additional security measures including regular privilege reviews, file integrity monitoring of critical system files, and enhanced access controls for monitoring infrastructure. Security teams should conduct comprehensive audits of all backend scripts and their included files to ensure no similar vulnerabilities exist within their monitoring environments. The remediation process should include verifying that files included by root-privileged scripts are properly protected and that the principle of least privilege is maintained throughout the system architecture. Additionally, organizations should consider implementing network segmentation and monitoring for unusual file modification activities that could indicate exploitation attempts, as this vulnerability represents a classic example of how insufficient file access controls can lead to complete system compromise.