CVE-2005-1205 in Windows
Summary
by MITRE
The Telnet client for Microsoft Windows XP, Windows Server 2003, and Windows Services for UNIX allows remote attackers 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 • 07/04/2025
The vulnerability described in CVE-2005-1205 represents a significant security flaw in the Telnet client implementation across multiple Microsoft Windows operating systems including Windows XP, Windows Server 2003, and Windows Services for UNIX. This issue specifically targets the Telnet protocol's handling of environment variables through the NEW-ENVIRON option, which is part of the Telnet protocol's negotiation mechanism for managing environment variables between client and server. The vulnerability stems from improper validation and handling of environment variable data during the Telnet session establishment process, creating an information disclosure channel that could be exploited by remote attackers.
The technical flaw manifests when a remote attacker crafts a malicious Telnet session negotiation sequence using the SEND ENV_USERVAR command within the NEW-ENVIRON option framework. This allows the attacker to request and receive sensitive environment variables from the target system that would normally be restricted or protected. The vulnerability operates at the protocol level within the Telnet implementation, specifically in how the client processes and responds to environment variable requests during the connection negotiation phase. This flaw essentially bypasses normal access controls and security boundaries that should prevent unauthorized access to system environment variables that may contain sensitive information such as paths, user identifiers, or other system configuration data.
The operational impact of this vulnerability extends beyond simple information disclosure, as the leaked environment variables could provide attackers with valuable reconnaissance data for subsequent exploitation attempts. Environment variables often contain system paths, configuration parameters, and user-specific information that could aid in crafting more sophisticated attacks or understanding the target system's configuration. Attackers could potentially use this information to identify system vulnerabilities, understand the deployment environment, or plan further infiltration activities. The vulnerability affects systems where Telnet is actively used for remote administration or access, making it particularly concerning for enterprise environments where legacy Telnet implementations may still be in use despite known security risks.
Mitigation strategies for this vulnerability should focus on eliminating the use of Telnet in favor of more secure remote access protocols such as SSH, which properly handles environment variables and provides encryption for all communication channels. Organizations should conduct thorough inventory assessments to identify all systems running Telnet services and ensure immediate patching or replacement of affected implementations. The vulnerability aligns with CWE-200, which covers "Information Exposure," and could potentially be leveraged as part of broader attack chains in the MITRE ATT&CK framework under the technique of "T1083: File and Directory Discovery" and "T1046: Network Service Scanning" where initial reconnaissance activities might involve gathering system information through protocol-level vulnerabilities. System administrators should also implement network segmentation and access controls to limit exposure of systems running Telnet services while ensuring that any remaining Telnet implementations are properly secured and monitored for unauthorized access attempts.