CVE-2000-0665 in Telsrv
Summary
by MITRE
GAMSoft TelSrv telnet server 1.5 and earlier allows remote attackers to cause a denial of service via a long username.
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Analysis
by VulDB Data Team • 10/13/2025
The vulnerability identified as CVE-2000-0665 affects GAMSoft TelSrv telnet server version 1.5 and earlier implementations, representing a classic buffer overflow condition that manifests through improper input validation. This flaw exists within the authentication handling mechanism of the telnet server where the system fails to adequately validate the length of username data submitted by remote clients. The vulnerability stems from insufficient bounds checking in the username processing routine, allowing an attacker to submit an excessively long username string that exceeds the allocated buffer space. When the telnet server attempts to process this malformed input, it overflows the designated memory buffer and subsequently crashes the service, resulting in a denial of service condition that prevents legitimate users from accessing the system. This issue directly maps to CWE-121, which describes stack-based buffer overflow conditions, and represents a fundamental weakness in input validation practices that has persisted across numerous network services.
The operational impact of this vulnerability extends beyond simple service disruption as it provides attackers with a reliable method to compromise system availability through minimal effort. Remote attackers can exploit this weakness without requiring authentication credentials or specialized tools, making it particularly dangerous in production environments where telnet services remain active. The denial of service condition affects the entire telnet server functionality, potentially impacting critical network infrastructure that relies on telnet for administrative access or legacy system management. Attackers can repeatedly exploit this vulnerability to maintain sustained disruption, creating a persistent availability threat that may go unnoticed if monitoring systems are not properly configured to detect service crashes or restarts. The vulnerability demonstrates how basic protocol implementations can contain fundamental security flaws that undermine system reliability and availability, aligning with ATT&CK technique T1499.1 which focuses on service stoppage and availability disruption through denial of service attacks.
Mitigation strategies for this vulnerability require immediate patching of the GAMSoft TelSrv software to version 1.5 or later, which contains the necessary buffer overflow protections and input validation mechanisms. Organizations should implement network segmentation to restrict access to telnet services and consider disabling telnet entirely in favor of more secure alternatives such as SSH protocols. Additional defensive measures include implementing rate limiting on authentication attempts, configuring intrusion detection systems to monitor for unusually long username strings, and establishing robust service monitoring to quickly detect and respond to service disruptions. Network administrators should also consider implementing automated service restart procedures to minimize the impact of successful exploitation attempts. The vulnerability highlights the importance of adhering to secure coding practices and conducting thorough input validation testing, particularly for network services that handle user-provided data. Organizations should regularly audit their network infrastructure for legacy services that may contain similar vulnerabilities and implement comprehensive vulnerability management programs to address such issues proactively. This case study emphasizes the critical need for proper buffer management and input validation in network service implementations, serving as a reminder that even seemingly simple protocol elements can contain dangerous security flaws that require careful attention to prevent exploitation.