CVE-2026-25084: ZLAN5143D Auth Bypass Vulnerability

CVE-2026-25084 Overview

CVE-2026-25084 is an authentication bypass vulnerability affecting the ZLAN5143D industrial device. The vulnerability allows attackers to bypass authentication mechanisms by directly accessing internal URLs, effectively circumventing security controls designed to protect the device's administrative interface and sensitive functions.

This vulnerability is classified under CWE-306 (Missing Authentication for Critical Function), indicating that the affected device fails to properly enforce authentication checks on certain internal endpoints. Attackers with network access to the device can exploit this flaw to gain unauthorized access to protected functionality without valid credentials.

Critical Impact

Unauthenticated remote attackers can bypass authentication entirely by directly accessing internal URLs, potentially leading to complete device compromise with full read, write, and administrative control over the ZLAN5143D device.

Affected Products

• ZLAN5143D Industrial Device

Discovery Timeline

• 2026-02-11 - CVE-2026-25084 published to NVD
• 2026-02-11 - Last updated in NVD database

Technical Details for CVE-2026-25084

Vulnerability Analysis

This authentication bypass vulnerability stems from missing authentication enforcement on internal URL endpoints within the ZLAN5143D device's web interface. The device exposes certain administrative and configuration endpoints that can be accessed directly without requiring prior authentication, effectively rendering the login mechanism ineffective for protecting sensitive operations.

Industrial devices like the ZLAN5143D are commonly deployed in operational technology (OT) environments where they serve as protocol converters or serial-to-Ethernet gateways. The ability to bypass authentication on such devices could allow attackers to manipulate device configurations, intercept or modify serial communications, or use the compromised device as a pivot point for further network intrusion.

Root Cause

The root cause of CVE-2026-25084 is the absence of proper authentication checks (CWE-306) on internal URL paths within the device's web server. The authentication mechanism appears to be implemented only at the main entry point (login page) but fails to validate session state or credentials when internal URLs are accessed directly. This architectural flaw allows attackers to bypass the intended security controls by crafting direct requests to protected endpoints.

Attack Vector

The attack vector for this vulnerability is network-based, requiring no user interaction and no prior privileges. An attacker with network access to the ZLAN5143D device can directly request internal URLs that should be protected by authentication. Since the device fails to verify authentication state on these endpoints, the attacker gains unauthorized access to administrative functions.

The exploitation process involves:

1. Network reconnaissance to identify the ZLAN5143D device on the target network
2. Enumeration of internal URLs through common path discovery techniques
3. Direct access to protected endpoints without authentication
4. Execution of privileged operations such as configuration changes, firmware manipulation, or data exfiltration

For detailed technical information about this vulnerability, refer to the CISA ICS Advisory.

Detection Methods for CVE-2026-25084

Indicators of Compromise

• Unexpected HTTP requests to internal administrative URLs on ZLAN5143D devices without preceding authentication
• Configuration changes on ZLAN5143D devices without corresponding authenticated login events
• Network traffic to ZLAN5143D management interfaces from unauthorized IP addresses

Detection Strategies

• Monitor web server logs on ZLAN5143D devices for direct access attempts to internal URLs without valid session tokens
• Deploy network intrusion detection systems (NIDS) with rules to detect unusual access patterns to known ZLAN5143D administrative endpoints
• Implement anomaly detection for HTTP traffic targeting industrial device management interfaces

Monitoring Recommendations

• Enable detailed logging on ZLAN5143D devices if supported and forward logs to a centralized SIEM
• Monitor network traffic to and from ZLAN5143D devices for unexpected administrative requests
• Establish baseline normal behavior for device access and alert on deviations
• Regularly audit device configurations for unauthorized changes

How to Mitigate CVE-2026-25084

Immediate Actions Required

• Restrict network access to ZLAN5143D devices using firewall rules and network segmentation
• Place ZLAN5143D devices behind VPN or other secure remote access solutions
• Disable direct internet exposure of affected devices
• Implement additional authentication layers at the network level where possible

Patch Information

At the time of publication, no vendor patch information is available in the CVE data. Organizations should contact ZLMCU through their official contact page to inquire about firmware updates or security patches addressing this vulnerability. Additional details may be available in the CISA ICS Advisory.

Workarounds

• Implement strict network segmentation to isolate ZLAN5143D devices from untrusted networks
• Deploy a reverse proxy with authentication enforcement in front of the device's web interface
• Use access control lists (ACLs) to limit which IP addresses can communicate with the device
• Monitor and audit all access to the device's management interface until a patch is available

# Example network segmentation using iptables
# Restrict access to ZLAN5143D device (example IP: 192.168.100.10) 
# to only authorized management workstation (192.168.1.50)

iptables -A FORWARD -s 192.168.1.50 -d 192.168.100.10 -p tcp --dport 80 -j ACCEPT
iptables -A FORWARD -d 192.168.100.10 -p tcp --dport 80 -j DROP