CVE-2002-1071 in Prestige
Summary
by MITRE
ZyXEL Prestige 642R allows remote attackers to cause a denial of service in the Telnet, FTP, and DHCP services (crash) via a TCP packet with both the SYN and ACK flags set.
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Analysis
by VulDB Data Team • 09/23/2024
The vulnerability identified as CVE-2002-1071 affects the ZyXEL Prestige 642R broadband router, representing a classic network protocol implementation flaw that enables remote attackers to execute denial of service attacks against critical services. This vulnerability specifically targets the router's handling of TCP packets, where the device fails to properly process TCP segments that simultaneously contain both the SYN and ACK flags set. The affected services include Telnet, FTP, and DHCP protocols, which are fundamental to router administration and network operations. The flaw demonstrates poor state machine implementation in the router's TCP stack, where the device does not properly validate incoming TCP packet headers before processing them. This vulnerability falls under the CWE-129 weakness category, which encompasses issues related to improper handling of input data, particularly in network protocol implementations. The ATT&CK framework categorizes this as a network service disruption technique, where adversaries exploit implementation flaws to render network services unavailable to legitimate users.
The technical exploitation of this vulnerability requires an attacker to send a specially crafted TCP packet that violates standard TCP protocol behavior. In normal TCP communication, a packet with both SYN and ACK flags set would typically indicate an error condition or an attempt at a TCP handshake attack such as a TCP SYN flood. However, the ZyXEL Prestige 642R router fails to properly handle this condition and instead crashes or becomes unresponsive when processing such packets. The router's TCP stack implementation lacks proper validation mechanisms to detect and reject malformed packets that could potentially cause memory corruption or state machine inconsistencies. This particular flaw represents a failure in input validation and protocol compliance, where the device does not implement proper TCP state transition checks that would normally be expected in robust network implementations. The crash affects multiple critical services because the TCP stack is a fundamental component that handles all network connections for the router's various services.
The operational impact of this vulnerability extends beyond simple service disruption, as it compromises the availability of essential network infrastructure services that administrators rely upon for router management and network operation. When the Telnet service crashes, network administrators lose remote access to configure and monitor the router, forcing them to rely on physical access methods that are time-consuming and disruptive. The FTP service crash affects file transfer capabilities that may be used for firmware updates or configuration file management. Most critically, the DHCP service disruption can cause complete network outages for devices that depend on automatic IP address assignment, potentially affecting numerous users and applications. This vulnerability essentially provides an attacker with a simple method to cause cascading failures across multiple network functions, making it particularly dangerous in enterprise environments where router availability is critical. The impact is amplified by the fact that these services are typically exposed to external networks, making the router an attractive target for automated scanning and exploitation.
Mitigation strategies for this vulnerability should focus on both immediate defensive measures and long-term architectural improvements. Network administrators should implement firewall rules that filter out TCP packets with both SYN and ACK flags set, effectively preventing exploitation attempts from reaching the router. The router firmware should be updated to a version that properly handles TCP packet validation and implements proper state machine transitions. Additionally, network segmentation should be employed to isolate the affected router from critical network segments, reducing the potential impact of successful exploitation. Monitoring systems should be configured to detect unusual TCP packet patterns that might indicate exploitation attempts. From a security architecture perspective, this vulnerability highlights the importance of implementing proper input validation and protocol compliance testing in network device firmware development. The vulnerability also underscores the need for network administrators to maintain current firmware versions and conduct regular security assessments of network infrastructure devices. Organizations should consider implementing intrusion detection systems that can identify and alert on TCP packet anomalies that match this vulnerability pattern, providing early warning of potential exploitation attempts.