CVE-2026-25817: HMS Networks Ewon RCE Vulnerability

CVE-2026-25817 Overview

HMS Networks Ewon Flexy and Cosy+ industrial gateways are affected by a command injection vulnerability (CWE-94) that allows remote code execution. The vulnerability stems from improper neutralization of special elements used in OS commands, enabling attackers with low privilege credentials to execute arbitrary commands on the affected gateway devices. This vulnerability impacts critical industrial remote access infrastructure commonly deployed in operational technology (OT) environments.

Critical Impact

Authenticated attackers with low-privilege access can achieve full remote code execution on HMS Networks Ewon Flexy and Cosy+ gateways, potentially compromising industrial control systems and operational technology environments.

Affected Products

• HMS Networks Ewon Flexy with firmware before 15.0s4
• HMS Networks Cosy+ with firmware 22.xx before 22.1s6
• HMS Networks Cosy+ with firmware 23.xx before 23.0s3

Discovery Timeline

• 2026-03-13 - CVE CVE-2026-25817 published to NVD
• 2026-03-16 - Last updated in NVD database

Technical Details for CVE-2026-25817

Vulnerability Analysis

This vulnerability is classified as improper neutralization of special elements used in an OS command (CWE-94: Improper Control of Generation of Code). The HMS Networks Ewon Flexy and Cosy+ gateways fail to properly sanitize user-controlled input before passing it to system command execution functions.

The vulnerability requires network access and valid credentials with low-level privileges on the gateway device. Once authenticated, an attacker can inject malicious OS commands through vulnerable input fields or API endpoints. The gateway processes these commands without adequate validation, resulting in arbitrary command execution with the privileges of the gateway application.

Industrial remote access gateways like the Ewon Flexy and Cosy+ series are commonly deployed to provide secure remote connectivity to programmable logic controllers (PLCs), human-machine interfaces (HMIs), and other industrial control system components. Successful exploitation could enable attackers to pivot into protected OT networks, manipulate industrial processes, or establish persistent access to critical infrastructure.

Root Cause

The root cause is insufficient input validation and sanitization in the firmware's command processing logic. User-supplied data is concatenated directly into OS command strings without proper escaping or allowlisting of permitted characters. This allows special shell metacharacters and command separators to be interpreted by the underlying operating system, breaking out of the intended command context.

Attack Vector

The attack is network-based and requires the attacker to possess valid credentials with low-privilege access to the gateway. The attacker authenticates to the device through its web interface or API, then submits specially crafted input containing OS command injection payloads. The malicious payload is processed by vulnerable firmware functions that execute the injected commands on the underlying system.

The vulnerability mechanism involves command injection through improperly sanitized input fields. When user-controlled data containing shell metacharacters (such as ;, |, $(), or backticks) reaches the command execution context, the injected commands are executed with the privileges of the gateway service. For detailed technical information, refer to the HMS Networks Security Advisory.

Detection Methods for CVE-2026-25817

Indicators of Compromise

• Unexpected outbound network connections from Ewon Flexy or Cosy+ devices to unknown IP addresses
• Anomalous process spawning or shell execution on gateway devices
• Authentication events followed by unusual API calls or configuration changes
• Presence of unexpected files or scripts on gateway filesystem
• Abnormal CPU or memory utilization on affected devices

Detection Strategies

• Monitor gateway logs for authentication events from unexpected sources or at unusual times
• Deploy network traffic analysis to detect command-and-control communications from industrial gateway segments
• Implement application-layer inspection on traffic to and from Ewon devices to identify injection patterns
• Correlate authentication logs with subsequent system command execution events

Monitoring Recommendations

• Enable comprehensive logging on all HMS Networks Ewon devices and forward logs to a SIEM
• Establish baseline behavior for gateway devices and alert on deviations
• Monitor for shell metacharacters in HTTP requests to gateway management interfaces
• Track firmware versions across all deployed Ewon devices to identify vulnerable instances

How to Mitigate CVE-2026-25817

Immediate Actions Required

• Upgrade Ewon Flexy firmware to version 15.0s4 or later immediately
• Upgrade Cosy+ firmware 22.xx to version 22.1s6 or later
• Upgrade Cosy+ firmware 23.xx to version 23.0s3 or later
• Review all user accounts on affected gateways and remove unnecessary privileges
• Audit recent authentication logs for signs of compromise

Patch Information

HMS Networks has released security patches addressing this vulnerability. Organizations should update affected devices to the following minimum firmware versions:

• Ewon Flexy: Firmware version 15.0s4 or later
• Cosy+ (22.xx branch): Firmware version 22.1s6 or later
• Cosy+ (23.xx branch): Firmware version 23.0s3 or later

Refer to the HMS Networks Security Advisory for detailed upgrade instructions and additional security recommendations.

Workarounds

• Restrict network access to gateway management interfaces using firewalls or VLANs
• Implement multi-factor authentication for gateway access where supported
• Place all industrial gateways behind a VPN and disable direct internet exposure
• Apply principle of least privilege to all gateway user accounts
• Monitor and log all administrative access to Ewon devices until patching is complete

# Network segmentation example - restrict gateway management access
# Add firewall rules to limit access to Ewon gateway management ports
iptables -A INPUT -p tcp --dport 443 -s 10.0.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP
iptables -A INPUT -p tcp --dport 80 -s 10.0.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP