CVE-2026-48550 in Nagios Core
Summary
by MITRE • 08/12/2026
Nagios Core before 4.5.14 and Nagios XI before 2026R1.7 are vulnerable to reflected cross-site scripting in cmd.cgi via the NagFormId parameter. An unauthenticated remote attacker can craft a malicious link that, when followed by an authenticated user, executes arbitrary JavaScript in the victim's browser.
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Analysis
by VulDB Data Team • 08/12/2026
The vulnerability described represents a critical reflected cross-site scripting flaw in Nagios Core and Nagios XI monitoring platforms, specifically affecting versions prior to 4.5.14 and 2026R1.7 respectively. This vulnerability resides within the cmd.cgi component which processes user input for command execution within the web interface. The issue manifests through the NagFormId parameter that fails to properly sanitize or validate incoming data before incorporating it into the HTTP response sent to users.
The technical nature of this flaw aligns with CWE-79, which describes cross-site scripting vulnerabilities where untrusted data is incorporated into web pages without proper validation or encoding. The reflected nature indicates that malicious input is immediately reflected back in the application's response, making this a server-side vulnerability that can be exploited through client-side interactions. Attackers can craft specially formatted URLs containing malicious JavaScript code within the NagFormId parameter, which when clicked by an authenticated user, executes within the victim's browser context with the privileges of that user.
The operational impact of this vulnerability is significant as it allows attackers to bypass authentication requirements entirely and execute arbitrary code in the victim's browser. An attacker can leverage this weakness to perform actions such as stealing session cookies, modifying data displayed in the monitoring interface, redirecting users to malicious sites, or even performing administrative actions if the victim has elevated privileges. This vulnerability particularly affects organizations that rely heavily on Nagios for system monitoring, as it provides a pathway for attackers to gain unauthorized access to critical infrastructure monitoring systems.
The attack vector requires social engineering to succeed, as an unauthenticated attacker must convince an authenticated user to click a malicious link. However, this makes the vulnerability particularly dangerous in environments where users frequently interact with web-based monitoring interfaces and may not be sufficiently security-aware to recognize suspicious links. The exploitation process typically involves crafting a URL that includes malicious JavaScript within the NagFormId parameter, which is then delivered through phishing emails, compromised websites, or other social engineering techniques.
Organizations should implement immediate mitigations including upgrading to patched versions of Nagios Core 4.5.14 and Nagios XI 2026R1.7, where proper input validation has been implemented. Additional protective measures include implementing content security policies that restrict script execution, enabling HTTPOnly flags on session cookies, and conducting regular security awareness training for users who interact with monitoring interfaces. Network-level protections such as web application firewalls can provide additional defense-in-depth, though the primary solution remains proper software patching and input validation as outlined in the ATT&CK framework's mitigation strategies for web application vulnerabilities.
The vulnerability demonstrates how seemingly minor input validation flaws can create significant security risks in enterprise monitoring systems where users frequently perform administrative tasks through web interfaces. This issue underscores the importance of comprehensive security testing including dynamic analysis of web applications, regular security audits, and adherence to secure coding practices that prevent injection vulnerabilities across all application components.