CVE-2005-1717 in ZyNOS
Summary
by MITRE
ZyXEL Prestige 650R-31 router running ZyNOS FW v3.40(KO.1) allows remote attackers to cause a denial of service (CPU consumption and network loss) via crafted fragmented IP packets.
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Analysis
by VulDB Data Team • 07/03/2019
The vulnerability identified as CVE-2005-1717 affects the ZyXEL Prestige 650R-31 router running ZyNOS firmware version 3.40(KO.1) and represents a significant denial of service weakness that can be exploited remotely through crafted fragmented internet protocol packets. This vulnerability falls under the broader category of network infrastructure security flaws that can severely impact network availability and reliability. The specific implementation flaw occurs within the router's packet processing mechanism where it fails to properly handle fragmented IP packets, leading to excessive cpu utilization and complete network disruption for connected devices. The attack vector is particularly concerning as it requires no authentication or specialized privileges to execute, making it accessible to any remote attacker with network access to the affected router.
The technical nature of this vulnerability stems from inadequate input validation and packet processing within the router's network stack implementation. When the router receives crafted fragmented ip packets, it fails to properly reconstruct or validate the fragments before processing them, causing the cpu to consume excessive resources in attempting to handle these malformed packets. This improper handling creates a resource exhaustion condition where the router's processing capabilities become overwhelmed, resulting in complete network service interruption. The vulnerability demonstrates a classic weakness in protocol implementation where the device does not properly account for edge cases in packet fragmentation handling, leading to a denial of service condition that affects legitimate network traffic. This flaw directly relates to CWE-129, which addresses improper validation of input boundaries, and CWE-400, which covers resource exhaustion vulnerabilities in network protocols.
The operational impact of this vulnerability extends beyond simple network disruption to encompass potential business continuity issues for organizations relying on the affected router. When exploited successfully, the attack causes sustained cpu consumption that can render the router completely unresponsive, leading to complete network outages for all devices connected to the affected network segment. The network loss experienced by end users can result in significant productivity losses and potential financial impacts, particularly in mission-critical environments where network availability is paramount. The remote nature of the attack means that adversaries can exploit this vulnerability from outside the network perimeter, making it particularly dangerous for organizations with exposed router configurations. This vulnerability also aligns with ATT&CK technique T1498, which covers network denial of service attacks, and represents a common exploitation pattern that has been documented in numerous network infrastructure security incidents throughout the years.
Mitigation strategies for this vulnerability require immediate firmware updates from ZyXEL to address the packet processing flaw in the affected ZyNOS firmware version. Organizations should implement network segmentation to isolate affected routers from critical network segments and deploy intrusion detection systems to monitor for unusual packet patterns that may indicate exploitation attempts. Network administrators should also consider implementing rate limiting or packet filtering rules to reduce the impact of fragment-based attacks, though these measures may not fully prevent the vulnerability. The most effective long-term solution involves upgrading to newer firmware versions that properly handle fragmented ip packets and have undergone security testing to prevent similar implementation flaws. Additionally, organizations should establish network monitoring procedures to detect unusual cpu utilization patterns that may indicate exploitation of this vulnerability, as the symptoms of the attack can be difficult to distinguish from other network performance issues without proper monitoring tools in place.