CVE-2000-0892 in Host
Summary
by MITRE
Some telnet clients allow remote telnet servers to request environment variables from the client that may contain sensitive information, or remote web servers to obtain the information via a telnet: URL.
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Analysis
by VulDB Data Team • 12/14/2024
The vulnerability described in CVE-2000-0892 represents a significant security flaw in telnet client implementations that enables remote servers to extract sensitive environment variables from connected clients. This weakness stems from the telnet protocol's design allowing remote servers to request specific client-side environment variables through the telnet negotiation process, creating an information disclosure risk that extends beyond traditional network boundaries. The vulnerability specifically affects telnet clients that fail to properly validate or restrict environment variable requests from remote servers, potentially exposing system configuration details, user contexts, and other sensitive data that could aid attackers in further compromising the affected systems.
The technical implementation of this vulnerability operates through the telnet protocol's negotiation mechanisms where remote servers can send environment variable requests using the telnet option negotiation sequence. When a telnet client receives such requests, it may respond with environment variables that contain sensitive information including but not limited to user names, system paths, terminal types, and other configuration details that could be leveraged for privilege escalation or targeted attacks. The flaw becomes particularly dangerous when telnet URLs are used in web browsers, as these can establish connections to remote servers that then request environment variables from the client system, effectively creating a vector for information leakage through web-based interfaces.
The operational impact of this vulnerability extends across multiple attack vectors and threat scenarios that align with several ATT&CK framework techniques including credential access and reconnaissance. Attackers can exploit this weakness to gather intelligence about target systems, potentially identifying user accounts, system configurations, and network topologies that would otherwise remain hidden. The vulnerability is particularly concerning in enterprise environments where telnet clients may be used in web applications or where legacy systems still rely on telnet protocols for remote access. This information disclosure can facilitate more sophisticated attacks including privilege escalation, lateral movement, and targeted exploitation of other system vulnerabilities that may be discovered through the leaked environment variables.
Mitigation strategies for CVE-2000-0892 should focus on implementing strict environment variable filtering and validation within telnet client implementations, ensuring that remote servers cannot request or receive sensitive system information without explicit user authorization. Organizations should disable unnecessary telnet functionality and migrate to more secure remote access protocols such as ssh, which do not exhibit this vulnerability. The implementation of proper access controls and network segmentation can help limit the exposure of telnet clients to untrusted remote servers. Additionally, security awareness training for administrators should emphasize the risks associated with legacy protocols and the importance of maintaining up-to-date security configurations. This vulnerability aligns with CWE-200 (Information Exposure) and represents a classic example of insufficient input validation where remote entities can manipulate client behavior to extract unintended information from the system environment.