CVE-2026-24789: Authentication Bypass Vulnerability

CVE-2026-24789 Overview

CVE-2026-24789 is a critical authentication bypass vulnerability affecting an industrial control device manufactured by ZLMCU. The vulnerability exists in an unprotected API endpoint that allows an attacker to remotely change the device password without providing any authentication credentials. This flaw represents a severe security risk as it enables complete unauthorized access to affected devices over the network.

Critical Impact

Unauthenticated attackers can remotely change device passwords, potentially gaining full administrative control over industrial control systems and disrupting critical operations.

Affected Products

• ZLMCU Industrial Control Devices (specific models not disclosed)
• Devices with exposed API endpoints accessible over the network

Discovery Timeline

• 2026-02-11 - CVE-2026-24789 published to NVD
• 2026-02-11 - Last updated in NVD database

Technical Details for CVE-2026-24789

Vulnerability Analysis

This vulnerability is classified as CWE-306 (Missing Authentication for Critical Function). The affected device exposes an API endpoint that handles password change operations without implementing proper authentication checks. This design flaw allows any network-accessible attacker to invoke the password change functionality and set arbitrary credentials on the device.

The vulnerability is particularly concerning in Industrial Control System (ICS) environments where these devices may be deployed. Successful exploitation could allow attackers to lock out legitimate administrators, establish persistent access, or use the compromised device as a pivot point for further attacks on the industrial network.

Root Cause

The root cause of this vulnerability is the absence of authentication mechanisms on a critical API endpoint responsible for password management. The device fails to verify the identity of the requesting party before processing password change requests, violating fundamental security principles for access control on administrative functions.

Attack Vector

The attack can be conducted remotely over the network without requiring any user interaction. An attacker with network access to the vulnerable device can send crafted HTTP requests to the unprotected API endpoint to change the device password. The attack requires no privileges, no authentication, and has low complexity.

The exploitation process involves identifying the vulnerable API endpoint and sending a password change request directly to it. Since no authentication is required, the attacker can set a password of their choosing, effectively taking over administrative control of the device.

For detailed technical information about this vulnerability, refer to the CISA ICS Advisory ICSA-26-041-02 and the associated CSAF document.

Detection Methods for CVE-2026-24789

Indicators of Compromise

• Unexpected password changes on ZLMCU industrial control devices
• Unauthorized API requests targeting password management endpoints
• Failed login attempts by legitimate administrators following credential changes
• Network traffic to device API endpoints from unexpected source IP addresses

Detection Strategies

• Monitor network traffic for unauthenticated requests to device management API endpoints
• Implement alerting for any password change events on critical ICS devices
• Deploy network intrusion detection systems (IDS) with rules targeting API abuse patterns
• Review device access logs for anomalous administrative operations

Monitoring Recommendations

• Establish baseline network communication patterns for ICS devices and alert on deviations
• Implement network segmentation monitoring to detect unauthorized access to ICS network zones
• Configure SIEM rules to correlate authentication failures with subsequent successful logins on ICS devices
• Deploy API gateway monitoring if devices are accessible through centralized management interfaces

How to Mitigate CVE-2026-24789

Immediate Actions Required

• Isolate affected ZLMCU devices from untrusted networks immediately
• Implement network segmentation to restrict API endpoint access to authorized management systems only
• Deploy firewall rules to block external access to device management interfaces
• Monitor affected devices for signs of compromise or unauthorized password changes

Patch Information

Contact ZLMCU directly for firmware updates or patches addressing this vulnerability. Vendor contact information is available at the ZLMCU Contact Page. Review the CISA ICS Advisory for the latest mitigation guidance and patch availability.

Workarounds

• Place affected devices behind a firewall that restricts access to the management API endpoint
• Implement VPN or other secure remote access mechanisms for device management
• Use network access control lists (ACLs) to whitelist only authorized management stations
• Consider deploying an API gateway or reverse proxy with authentication enforcement

# Example firewall rule to restrict API access (adapt to your environment)
# Allow management access only from authorized IP range
iptables -A INPUT -p tcp --dport 80 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP