CVE-1999-1336 in HiperARC
Summary
by MITRE
3Com HiPer Access Router Card (HiperARC) 4.0 through 4.2.29 allows remote attackers to cause a denial of service (reboot) via a flood of IAC packets to the telnet port.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 04/19/2026
The vulnerability identified as CVE-1999-1336 affects the 3Com HiPer Access Router Card (HiperARC) version 4.0 through 4.2.29, representing a significant security flaw in network infrastructure equipment that enables remote attackers to execute denial of service attacks. This vulnerability specifically targets the telnet service running on the affected router cards, exploiting a weakness in how the system handles incoming network traffic. The flaw manifests when an attacker floods the telnet port with IAC (Interpret As Command) packets, which are part of the telnet protocol's control mechanism designed to negotiate terminal parameters and options between client and server. The vulnerability stems from inadequate input validation and error handling within the telnet implementation, allowing malformed or excessive IAC sequences to trigger unexpected behavior in the router's processing logic. This particular flaw falls under the category of insufficient input validation as classified by CWE-20, where the system fails to properly validate or sanitize input data before processing it, leading to system instability and potential service disruption.
The operational impact of this vulnerability extends beyond simple service interruption, as it provides attackers with a means to repeatedly disrupt network connectivity for systems relying on these router cards for access and communication. When the telnet service becomes unresponsive due to the flood of IAC packets, the affected router card undergoes an automatic reboot process, effectively cutting off network access for all connected devices. This disruption can have cascading effects on network infrastructure, particularly in environments where these router cards serve as critical access points or gateway devices. The vulnerability is particularly concerning because it requires no authentication to exploit, making it accessible to anyone with network access to the affected system. From an attack perspective, this represents a straightforward but effective method of network disruption that aligns with the tactics described in the MITRE ATT&CK framework under the 'Denial of Service' technique, specifically targeting network services through protocol manipulation. The attack vector operates at the network layer, exploiting weaknesses in the telnet protocol implementation rather than targeting application-level vulnerabilities or exploiting system-level weaknesses.
The mitigation strategies for this vulnerability focus on both immediate defensive measures and long-term architectural improvements. Network administrators should implement rate limiting or packet filtering rules to restrict the volume of IAC packets that can reach the telnet service, effectively preventing the flood attack from overwhelming the system. Additionally, disabling the telnet service entirely and migrating to more secure protocols such as SSH (Secure Shell) provides a robust solution that eliminates the vulnerability while maintaining necessary remote access capabilities. The affected 3Com HiperARC devices should be updated to versions that properly handle IAC packet sequences and implement appropriate input validation. Organizations should also consider implementing network segmentation and monitoring solutions to detect unusual traffic patterns that might indicate exploitation attempts. The vulnerability highlights the importance of proper protocol implementation and input validation in network services, as outlined in security standards such as the OWASP Top Ten and NIST cybersecurity frameworks. Regular security assessments and vulnerability scanning should be conducted to identify similar weaknesses in other network infrastructure components, ensuring comprehensive protection against similar attacks that exploit protocol-level vulnerabilities.