CVE-2002-0438 in ZyWALL 10
Summary
by MITRE
ZyXEL ZyWALL 10 before 3.50 allows remote attackers to cause a denial of service via an ARP packet with the firewall s IP address and an incorrect MAC address, which causes the firewall to disable the LAN interface.
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Analysis
by VulDB Data Team • 12/27/2024
The vulnerability identified as CVE-2002-0438 affects ZyXEL ZyWALL 10 firewalls running firmware versions prior to 3.50, representing a significant denial of service weakness in network security infrastructure. This flaw manifests when the firewall receives an ARP packet containing its own IP address but with an incorrect MAC address, triggering an unexpected behavioral response that disables the LAN interface. The attack vector is entirely remote, requiring no physical access or authentication credentials, making it particularly dangerous for network administrators who may not immediately detect the compromise. This vulnerability directly impacts the availability of network services by rendering the firewall incapable of processing traffic on its local area network interface, effectively creating a network outage that can span entire organizational networks depending on the firewall's role.
The technical mechanism behind this vulnerability stems from the firewall's inadequate handling of ARP protocol messages, specifically its failure to properly validate the relationship between IP addresses and MAC addresses within ARP packets. When the ZyWALL 10 receives an ARP packet with its own IP address but a mismatched MAC address, the device's ARP table processing logic incorrectly interprets this as a security threat or network anomaly, leading to the automatic disabling of the LAN interface as a protective measure. This behavior violates the expected ARP protocol behavior where devices should maintain proper address resolution tables and not disable network interfaces based on malformed ARP packets. The vulnerability demonstrates a classic lack of proper input validation and error handling within the firewall's network protocol processing stack, which is classified under CWE-248 as an "Uncaught Exception" and potentially CWE-347 as "Improper Verification of Cryptographic Signature" if the device employs any cryptographic verification mechanisms. From an operational perspective, this vulnerability creates a scenario where an attacker can remotely disrupt network services by simply sending a single crafted ARP packet, making it a preferred method for network disruption attacks.
The operational impact of this vulnerability extends beyond simple network disruption to encompass broader security implications for organizations relying on ZyXEL ZyWALL 10 firewalls. When the LAN interface becomes disabled, all network traffic destined for or originating from the local network segment is blocked, potentially affecting business operations, employee productivity, and critical infrastructure connectivity. The vulnerability's remote exploitability means that attackers can target multiple firewalls simultaneously without physical presence, creating a scalable attack vector that could affect entire corporate networks. Network administrators may struggle to diagnose the issue since the firewall's normal operation appears functional while the specific interface is disabled, leading to extended downtime and increased incident response costs. This vulnerability aligns with ATT&CK technique T1498 as "Network Denial of Service" and potentially T1566 as "Phishing for Information" if attackers use this vulnerability as part of a broader attack chain. The flaw also represents a failure in the principle of least privilege and fail-safe design, as the firewall should maintain network availability even when processing potentially malicious packets. Organizations with multiple ZyWALL 10 devices would be particularly vulnerable to coordinated attacks, as the same exploit could disable multiple network segments simultaneously, creating cascading failures across network infrastructure.
Mitigation strategies for CVE-2002-0438 should prioritize immediate firmware updates to version 3.50 or later, which contain the necessary patches to properly handle ARP packet validation without disabling network interfaces. Network administrators should implement ARP inspection mechanisms and monitoring systems that can detect anomalous ARP traffic patterns, providing early warning of potential exploitation attempts. The firewall's ARP table management should be configured to maintain more robust validation procedures, ensuring that legitimate ARP requests are processed while anomalous packets are handled gracefully without network interface disruption. Organizations should also consider implementing network segmentation strategies to limit the impact of such attacks, ensuring that the compromise of one firewall does not affect the entire network infrastructure. Regular network monitoring and intrusion detection systems should be configured to alert on unusual ARP traffic patterns that could indicate exploitation attempts, while access controls should be implemented to limit who can configure ARP-related settings on firewall devices. The vulnerability serves as a reminder of the critical importance of maintaining up-to-date network security equipment and implementing proper network hygiene practices to prevent exploitation of known vulnerabilities.