CVE-2026-31981: Stored HTML Injection in Nozomi Networks CMC and Guardian

Technical summary

CVE-2026-31981 is a stored cross-site scripting (XSS) vulnerability rooted in insufficient input validation in a shared validation function used by the Diagram tab and Graph view components in Nozomi Networks CMC and Guardian. An authenticated user with administrative privileges can inject malicious HTML tags into N2OS configuration data through multiple input vectors. The injected content persists in the configuration and renders client-side when viewed by other users. The vulnerability is partially mitigated by existing Content Security Policy (CSP) configuration and additional input validation that prevent full XSS exploitation and direct information disclosure, but stored HTML injection remains viable for attacks like phishing and open redirects.

Business impact

The primary business risk is credential compromise through phishing attacks embedded in legitimate-looking configuration views. An adversary with administrative access (either through compromise or insider threat) can inject malicious HTML to deceive other users into disclosing credentials or visiting attacker-controlled sites. This could lead to lateral movement within the network monitoring infrastructure, unauthorized changes to monitoring policies, or disruption of visibility into critical operational technology environments. The medium CVSS score reflects the requirement for high-privilege access and user interaction, but the damage potential in OT/network security contexts warrants prompt remediation.

Affected systems

Nozomi Networks CMC and Guardian are affected. Both products use the same insufficiently restrictive input validation function that fails to properly sanitize HTML in the Diagram tab and Graph view. Organizations deploying these network security and monitoring solutions should assess their administrative access controls and user awareness to determine exposure.

Exploitability

Exploitation requires authenticated administrative privileges, making it unsuitable for unauthenticated attacks but relevant for insider threat and account compromise scenarios. The attack requires a victim to view the poisoned configuration data in the Diagram tab or Graph view, introducing a user interaction requirement. Existing CSP policies and additional validation prevent escalation to full XSS with script execution or data exfiltration, narrowing the attack surface to HTML-based phishing and redirect attacks. Overall exploitability is constrained but not negligible in high-risk environments.

Remediation

Contact Nozomi Networks for patched versions of CMC and Guardian that strengthen input validation in the shared validation function. Interim mitigations include restricting administrative access to only trusted users, monitoring configuration change logs for suspicious HTML patterns, and educating users to verify URLs and requests before clicking links in configuration views. Verify against the vendor advisory for specific patched version numbers and deployment guidance.

Patch guidance

Patches are available from Nozomi Networks for both CMC and Guardian products. Consult the vendor advisory and security bulletins for specific patch version numbers and deployment procedures. Test patches in a non-production environment first, as these products are critical to network monitoring and visibility. Coordinate patching with change control processes to minimize disruption to OT visibility.

Detection guidance

Monitor N2OS configuration files and database logs for HTML tags (e.g., <script>, <img>, <iframe>, <a>) in fields not expected to contain markup, particularly in Diagram and Graph view configuration data. Web application firewalls and endpoint detection systems should flag unusual HTML injection patterns in configuration submissions. Review administrative user activity logs for changes to configuration data, and correlate with phishing complaints or suspicious user behavior. Implement integrity checks or hashing of configuration baselines to detect unauthorized modifications.

Why prioritize this

Although the CVSS score is medium (5.9), prioritization should account for the OT/network security context. Nozomi products are often deployed as critical visibility tools in industrial and operational technology environments. A compromise of administrative accounts or insider threats could weaponize this vulnerability to deceive operators or security teams. Organizations with mature admin access controls and security awareness can deprioritize slightly; those with weaker access governance should treat this as higher priority. The lack of current exploitation in the wild (no KEV listing) provides a window for orderly patching.

Risk score, explained

The CVSS 3.1 score of 5.9 (MEDIUM) reflects the following factors: Network-accessible attack vector, low attack complexity, high privileges required, and requirement for user interaction. Confidentiality, integrity, and availability impacts are all rated as low because CSP and additional input validation prevent direct information disclosure and script execution. However, the impact is rated as 'Scope Changed' (affecting resources beyond the vulnerable component) because phishing and redirect attacks can affect users outside the immediate application. The score appropriately penalizes the high privilege requirement while recognizing the real risk of HTML injection for social engineering.

Frequently asked questions