CVE-2002-1911 in ZoneAlarm
Summary
by MITRE
ZoneAlarm Pro 3.0 and 3.1, when configured to block all traffic, allows remote attackers to cause a denial of service (CPU and memory consumption) via a large number of SYN packets (SYN flood). NOTE: the vendor was not able to reproduce the issue.
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Analysis
by VulDB Data Team • 05/17/2025
The vulnerability identified as CVE-2002-1911 affects ZoneAlarm Pro version 3.0 and 3.1 firewall software when configured with strict traffic blocking policies. This represents a critical denial of service weakness that exploits the software's handling of network connection requests. The flaw manifests when the firewall encounters an excessive volume of SYN packets, which are the initial packets in the TCP three-way handshake process. When configured to block all traffic, ZoneAlarm Pro fails to properly manage these connection attempts, leading to resource exhaustion that can severely impact system performance and availability.
The technical implementation of this vulnerability stems from inadequate packet processing logic within the firewall's network stack handling. SYN flood attacks are a well-known form of denial of service attack that exploits the TCP protocol's connection establishment process by sending a large number of SYN requests without completing the handshake. The ZoneAlarm Pro software demonstrates a failure in its resource management and connection tracking mechanisms, causing it to consume excessive CPU cycles and memory resources when processing these malformed or excessive connection attempts. This behavior aligns with CWE-400, which categorizes unchecked resource consumption as a significant security weakness. The vulnerability essentially creates a resource exhaustion condition where legitimate system resources become unavailable due to the software's inability to properly handle high-volume network traffic patterns.
From an operational perspective, this vulnerability poses a substantial risk to network security infrastructure, particularly in environments where ZoneAlarm Pro serves as a primary firewall solution. The attack vector requires only that remote adversaries send a large volume of SYN packets to trigger the denial of service condition, making it relatively easy to exploit. The impact extends beyond simple service disruption to potentially compromise the entire network security posture, as the firewall becomes unavailable to protect against other threats. This vulnerability demonstrates the critical importance of proper resource management in security software, as a defensive tool becomes a potential attack vector when not properly implemented. The issue also highlights the challenges in testing and validating security products under realistic attack conditions, as the vendor was unable to reproduce the problem, suggesting potential gaps in their testing methodologies.
The mitigation strategies for this vulnerability require immediate attention from affected organizations, including implementing network-level protections such as SYN cookies or rate limiting to prevent the attack from reaching the vulnerable firewall. System administrators should also consider updating to newer versions of ZoneAlarm Pro where the issue has been addressed, though the vendor's inability to reproduce the issue raises concerns about the reliability of their patch validation process. Network segmentation and intrusion detection systems can provide additional layers of protection by monitoring for unusual traffic patterns that might indicate a SYN flood attack. This vulnerability also emphasizes the need for comprehensive security testing including stress testing and penetration testing that simulates real-world attack conditions. Organizations should follow ATT&CK framework guidance for network denial of service attacks, particularly focusing on techniques related to resource exhaustion and connection manipulation. The incident underscores the importance of maintaining up-to-date security software and implementing defensive measures that can protect against both known and unknown vulnerabilities in network security infrastructure.