CVE-2025-13940 is a vulnerability classified under CWE-440 (Expected Behavior Violation) affecting WatchGuard Fireware OS, specifically versions from 12.8.1 through 12.11.4 and 2025.1 through 2025.1.2. The flaw allows an attacker with high privileges on the device to bypass the boot time system integrity check, a critical security mechanism designed to verify the integrity of the system before fully booting. Normally, if the integrity check fails, the Firebox device is expected to shut down to prevent operation under potentially compromised conditions. However, due to this vulnerability, the attacker can prevent the device from shutting down despite integrity check failures, effectively allowing the device to operate in an untrusted state. The on-demand integrity check accessible via the Fireware Web UI still correctly reports failures, but this does not mitigate the risk posed by the boot-time bypass. The vulnerability requires local access with high privileges (e.g., administrative or root-level access) and does not require user interaction, making remote exploitation unlikely without prior compromise. The CVSS 4.0 base score is 6.7 (medium severity), reflecting the moderate impact and exploitation complexity. No known public exploits or active exploitation have been reported to date. The issue could be leveraged by attackers to maintain persistence, deploy malicious firmware or software modifications, or evade detection mechanisms that rely on boot-time integrity verification.

For European organizations using WatchGuard Firebox devices running the affected Fireware OS versions, this vulnerability poses a risk to the integrity and trustworthiness of their network security infrastructure. Firebox devices are commonly deployed as network firewalls, VPN gateways, and unified threat management appliances, making them critical for perimeter defense and secure remote access. If an attacker gains high-level access to these devices, they could bypass boot-time integrity checks and maintain persistent, undetected control over the device. This could lead to unauthorized network access, data interception, or disruption of security monitoring. The inability of the device to shut down upon integrity failure could allow compromised devices to continue operating, increasing the risk of lateral movement and further compromise within the network. Given the importance of these devices in protecting sensitive data and critical infrastructure, the vulnerability could have significant operational and reputational impacts. However, the requirement for high privileges and local access limits the likelihood of widespread exploitation without prior compromise. European organizations in sectors such as finance, government, telecommunications, and critical infrastructure, where WatchGuard devices are prevalent, should be particularly vigilant.

European organizations should prioritize upgrading affected Fireware OS versions to patched releases once available from WatchGuard, as no patch links are currently provided. Until patches are released, organizations should implement strict access controls to limit administrative access to Firebox devices, including network segmentation, multi-factor authentication, and monitoring for unusual administrative activity. Regularly perform on-demand system integrity checks via the Fireware Web UI to detect any integrity failures promptly. Employ robust endpoint and network detection mechanisms to identify signs of compromise or unauthorized changes to Firebox devices. Consider implementing additional physical security controls to prevent unauthorized local access to devices. Maintain up-to-date backups of device configurations to enable rapid recovery if compromise is detected. Engage with WatchGuard support or security advisories for updates on patches or workarounds. Finally, conduct security awareness training for administrators to recognize and respond to suspicious device behavior or integrity alerts.