CVE-2005-0488 in Kerberos
Summary
by MITRE
Certain BSD-based Telnet clients, including those used on Solaris and SuSE Linux, allow remote malicious Telnet servers to read sensitive environment variables via the NEW-ENVIRON option with a SEND ENV_USERVAR command.
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Analysis
by VulDB Data Team • 01/23/2025
The vulnerability described in CVE-2005-0488 represents a significant security flaw in telnet client implementations across various BSD-based systems including Solaris and SuSE Linux distributions. This weakness stems from improper handling of the NEW-ENVIRON option within the telnet protocol specification, which creates an avenue for remote attackers to extract sensitive system information through crafted telnet server responses. The vulnerability specifically manifests when telnet clients process the SEND ENV_USERVAR command, allowing malicious servers to access and potentially exfiltrate environment variables containing confidential data. This issue affects the fundamental security model of telnet communications where clients trust server responses without adequate validation mechanisms.
The technical root cause of this vulnerability lies in the implementation of the telnet protocol's NEW-ENVIRON option handling within affected telnet clients. When a telnet client receives a NEW-ENVIRON option response containing environment variable data, it fails to properly sanitize or validate the incoming information before processing it. The SEND ENV_USERVAR command specifically targets user-defined environment variables that may contain sensitive information such as authentication tokens, system paths, or other confidential data. This flaw aligns with CWE-200, which addresses the exposure of sensitive information, and represents a classic case of insufficient input validation and sanitization in network protocol implementations. The vulnerability operates at the application layer of the network stack, making it particularly dangerous as it can be exploited without requiring elevated privileges or complex attack vectors.
The operational impact of CVE-2005-0488 extends beyond simple information disclosure, as the exposed environment variables can provide attackers with valuable intelligence for subsequent attacks. When malicious telnet servers can access variables containing authentication credentials, system paths, or other sensitive configuration data, they gain significant advantages in planning further exploitation attempts. The vulnerability affects systems where telnet clients are used for remote administration or system access, particularly in enterprise environments where legacy telnet implementations may still be in use. This issue demonstrates the importance of proper protocol implementation and the dangers of trusting remote server responses without adequate security controls. The attack vector is particularly concerning because it can be executed remotely without requiring local system access, making it an attractive target for attackers seeking to gather intelligence before launching more sophisticated attacks.
Mitigation strategies for this vulnerability should focus on both immediate remediation and long-term architectural improvements. The most effective immediate solution involves updating telnet client implementations to properly validate and sanitize environment variable data received through the NEW-ENVIRON option. System administrators should also consider implementing network-level controls such as firewalls to restrict telnet traffic to trusted networks and disable unnecessary telnet services. Organizations should transition away from telnet protocols entirely in favor of more secure alternatives like SSH, which provide better encryption and authentication mechanisms. The vulnerability highlights the importance of adhering to security best practices outlined in the ATT&CK framework, particularly in the area of credential access and defense evasion techniques. Regular security assessments and vulnerability scanning should be conducted to identify similar protocol implementation flaws across the enterprise network infrastructure, ensuring that legacy systems are properly secured or migrated to more secure communication protocols.