CVE-2026-25819 is a denial of service vulnerability identified in HMS Networks Ewon Flexy and Cosy+ devices running firmware versions prior to 15.0s4 for Flexy, 22.1s6 for Cosy+ 22.xx, and 23.0s3 for Cosy+ 23.xx. The vulnerability arises from improper handling of specially crafted HTTP requests directed at the device's graphical user interface (GUI). An unauthenticated attacker with network access to the device's GUI can send these malicious requests, causing the device to reboot unexpectedly. This reboot disrupts the device's normal operation, leading to denial of service conditions. The vulnerability does not require authentication or user interaction beyond access to the GUI, which may be exposed on internal networks or, if misconfigured, on external networks. The affected devices are commonly used in industrial automation, remote monitoring, and IoT environments, where continuous availability is critical. No public exploits have been reported yet, but the vulnerability is publicly disclosed and patched in firmware versions 15.0s4 (Flexy), 22.1s6 (Cosy+ 22.xx), and 23.0s3 (Cosy+ 23.xx). The lack of a CVSS score necessitates an independent severity assessment based on the impact on availability, ease of exploitation, and scope of affected systems.

The primary impact of CVE-2026-25819 is denial of service through forced device reboots, which can interrupt critical industrial and remote monitoring operations relying on Ewon Flexy and Cosy+ devices. Such disruptions can lead to loss of operational visibility, delayed response to industrial events, and potential safety risks in automated environments. Organizations using these devices in manufacturing, energy, utilities, and infrastructure sectors may experience operational downtime and reduced reliability. Since the vulnerability requires only network access to the device's GUI and no authentication, attackers with network presence can exploit it relatively easily. This increases the risk of targeted attacks or opportunistic scanning in environments where these devices are deployed. Although no exploits are currently known in the wild, the public disclosure may prompt attackers to develop exploit code. The scope includes all affected firmware versions, which may be widely deployed globally in industrial control systems and IoT networks.

To mitigate CVE-2026-25819, organizations should immediately verify the firmware versions of their HMS Networks Ewon Flexy and Cosy+ devices and upgrade to the fixed versions: 15.0s4 or later for Flexy, 22.1s6 or later for Cosy+ 22.xx, and 23.0s3 or later for Cosy+ 23.xx. Network segmentation should be enforced to restrict access to the device GUI interfaces only to trusted internal networks and authorized personnel. Implement firewall rules or VPN access controls to prevent unauthorized external access to the device management interfaces. Regularly audit device configurations to ensure no unintended exposure of the GUI to public networks. Monitor network traffic for unusual HTTP requests targeting these devices as an early indicator of exploitation attempts. Additionally, maintain an inventory of all deployed Ewon devices to ensure comprehensive patch management. Consider deploying intrusion detection systems capable of recognizing anomalous HTTP requests to these devices. Finally, establish incident response procedures to quickly address any device reboots or availability issues.