A critical vulnerability, CVE-2026-54402, has been identified in several UniFi products, including UniFi OS, UniFi Dream Machine, Enterprise Fortress Gateway, UniFi Dream Router, and UniFi Dream Machine Pro. This vulnerability stems from an improper input validation flaw that enables a malicious actor with network access and low privileges to execute arbitrary commands on the host device. With a CVSS score of 9.9, this represents a critical risk to affected systems. The potential for remote code execution poses significant security risks, including unauthorized access, data exfiltration, and disruption of services. Organizations utilizing these devices are strongly advised to apply the latest security patches provided by the vendor to mitigate this threat. Until patches are applied, network administrators should implement strict access controls and monitor for suspicious activity to reduce the likelihood of exploitation. This vulnerability underscores the importance of maintaining up-to-date firmware and adhering to secure configuration practices.