CVE-2026-48553 in Nagios Core
Summary
by MITRE • 08/12/2026
Nagios Core before 4.5.13 and Nagios XI before 2026R1.5 are vulnerable to authenticated remote code execution via custom-variable macro injection through the Nagios Remote Data Processor (NRDP). When a custom variable defined on a host, service, or contact is referenced in a shell-executed command line, an authenticated attacker with NRDP access can inject OS commands through the macro value. Exploitation requires a non-default configuration in which a custom variable is defined and referenced in a shell-executed command.
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Analysis
by VulDB Data Team • 08/12/2026
The vulnerability under discussion represents a critical authenticated remote code execution flaw affecting Nagios Core versions prior to 4.5.13 and Nagios XI versions prior to 2026R1.5. This security weakness resides within the Nagios Remote Data Processor component and specifically exploits macro injection techniques that leverage custom variable handling in shell command execution contexts. The vulnerability operates through a sophisticated chain of exploitation where an authenticated attacker with access to NRDP can manipulate custom variables defined on hosts, services, or contacts to inject malicious operating system commands. This represents a classic example of command injection vulnerability that falls under CWE-77 and aligns with ATT&CK technique T1059.001 for command and scripting interpreter. The flaw requires a specific non-default configuration scenario where custom variables are explicitly defined and subsequently referenced within shell-executed command lines, making the exploitation dependent on particular deployment setups rather than default configurations.
The technical implementation of this vulnerability stems from insufficient input validation and sanitization of custom variable values when these variables are processed in shell contexts. When Nagios processes commands that reference custom variables through macro expansion, it fails to properly escape or sanitize special shell characters that could allow command injection attacks. This occurs particularly when the NRDP component handles data containing custom variable definitions that are later expanded into shell execution contexts. The attack vector requires an authenticated session with NRDP access, which means that the attacker must already have legitimate credentials or have obtained them through other means. The exploitation process involves crafting malicious input within the custom variable fields such that when the macro expansion occurs during command execution, additional commands are interpreted by the shell as part of the original command line. This vulnerability demonstrates the dangerous intersection between configuration management and shell command execution in monitoring systems.
The operational impact of this vulnerability extends beyond simple privilege escalation to potentially enable full system compromise when exploited successfully. An authenticated attacker could execute arbitrary code with the privileges of the Nagios service account, which typically runs with elevated permissions to monitor system resources and execute various commands. The consequences include potential data exfiltration, system reconnaissance, lateral movement within network environments, and establishment of persistent access points through backdoor installations. Organizations relying on Nagios for critical infrastructure monitoring face significant risk if this vulnerability remains unpatched, as it could allow attackers to gain complete control over monitoring capabilities while maintaining operational stealth. The vulnerability's exploitation requires specific conditions, but once achieved, it provides attackers with substantial operational flexibility and persistence mechanisms that align with ATT&CK tactic TA0003 (Persistence) and TA0004 (Privilege Escalation).
Mitigation strategies for this vulnerability center around immediate patching of affected Nagios installations to versions 4.5.13 or later for Core and 2026R1.5 or later for XI. Organizations should also implement network segmentation to limit access to NRDP components, enforce strict authentication controls, and monitor for suspicious macro usage patterns in command execution logs. Additionally, security teams should review custom variable configurations to ensure that variables are properly sanitized before shell execution contexts. The implementation of principle of least privilege access controls for NRDP endpoints and regular security audits of monitoring system configurations can significantly reduce the attack surface. Organizations should also consider implementing web application firewalls or intrusion detection systems to monitor for command injection patterns in network traffic related to Nagios NRDP communications. This vulnerability highlights the importance of secure coding practices in monitoring systems and demonstrates how seemingly innocuous configuration features can become security gateways when not properly validated against shell execution contexts.