CVE-2000-0896 in SOHO Firewall
Summary
by MITRE
WatchGuard SOHO firewall allows remote attackers to cause a denial of service via a flood of fragmented IP packets, which causes the firewall to drop connections and stop forwarding packets.
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Analysis
by VulDB Data Team • 04/09/2019
The CVE-2000-0896 vulnerability affects WatchGuard SOHO firewalls, representing a classic denial of service attack vector that exploits weaknesses in IP packet handling mechanisms. This vulnerability demonstrates how fundamental network protocols can be leveraged to disrupt critical security infrastructure, particularly impacting small office home office environments that rely on these devices for network protection. The flaw specifically targets the firewall's ability to process fragmented internet protocol packets, which are legitimate network constructs used to transmit data larger than the maximum transmission unit of a network segment. When subjected to excessive fragmentation, the firewall's processing capabilities become overwhelmed, leading to complete service disruption.
The technical implementation of this vulnerability stems from inadequate input validation and resource management within the firewall's packet processing engine. Attackers can exploit this weakness by flooding the network with carefully crafted fragmented IP packets that trigger a cascading failure in the firewall's connection handling mechanisms. The attack exploits the fact that fragmented packets require additional processing overhead as the firewall must reassemble them before inspection, creating a resource exhaustion scenario where legitimate network traffic is blocked while the system attempts to process malicious fragments. This vulnerability falls under the category of resource exhaustion attacks and demonstrates poor handling of network protocol edge cases, which aligns with CWE-400 - Uncontrolled Resource Consumption and CWE-113 - Improper Neutralization of CRLF Sequences in HTTP Headers.
From an operational impact perspective, this vulnerability poses significant risks to organizations relying on WatchGuard SOHO firewalls for network security. The denial of service condition affects not only the firewall's ability to forward legitimate packets but also disrupts all network connectivity for users behind the device, effectively creating a complete network outage. The attack can be executed with minimal resources, making it particularly dangerous as even a single attacker can render the entire network infrastructure unusable. Network administrators face the challenge of detecting such attacks, as they may appear as normal traffic patterns while simultaneously causing operational disruption. This vulnerability represents a critical weakness in network security infrastructure that directly impacts business continuity and network availability.
Mitigation strategies for CVE-2000-0896 should focus on both immediate protective measures and long-term architectural improvements. Organizations should implement rate limiting and packet filtering rules to restrict the number of fragmented packets that can be processed within a given time window, effectively preventing the resource exhaustion attack. Network segmentation and the implementation of upstream filtering can help reduce the attack surface by limiting direct access to the vulnerable firewall. Additionally, upgrading to newer firmware versions that address the fragmentation handling issues represents the most effective long-term solution. The implementation of intrusion detection systems can provide early warning of such attacks, allowing administrators to take defensive measures before complete service disruption occurs. This vulnerability highlights the importance of robust input validation and resource management in security appliances, as outlined in the ATT&CK framework under T1498 - Network Denial of Service, which emphasizes the need for resilient network infrastructure against such attacks. Organizations should also consider implementing redundant network security measures to ensure that single points of failure like this vulnerability do not result in complete network outages.