CVE-2001-0347 in Windows
Summary
by MITRE
Information disclosure vulnerability in Microsoft Windows 2000 telnet service allows remote attackers to determine the existence of user accounts such as Guest, or log in to the server without specifying the domain name, via a malformed userid.
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Analysis
by VulDB Data Team • 10/06/2025
The vulnerability described in CVE-2001-0347 represents a critical information disclosure flaw within the Microsoft Windows 2000 telnet service implementation. This vulnerability specifically targets the authentication handling mechanism of the telnet service, which was widely deployed in enterprise environments during the early 2000s. The flaw stems from inadequate input validation and error handling within the telnet protocol implementation, creating a pathway for remote attackers to gather sensitive information about system user accounts. The vulnerability operates at the application layer of the network stack, leveraging the telnet service's response behavior to reveal account existence information.
The technical exploitation of this vulnerability occurs through the manipulation of userid parameters during the telnet authentication process. When a malformed userid is submitted to the telnet service, the system's response varies depending on whether the account exists or not. This differential response behavior creates a timing or error code difference that attackers can observe and analyze to determine the existence of specific user accounts such as the well-known Guest account. The vulnerability is particularly dangerous because it allows attackers to perform account enumeration without requiring any prior authentication credentials or privileged access to the system. This behavior directly violates the principle of least privilege and demonstrates a fundamental flaw in the service's security design.
The operational impact of CVE-2001-0347 extends beyond simple information disclosure, as it provides attackers with crucial reconnaissance data that can be leveraged for subsequent attacks. The ability to enumerate user accounts without authentication creates a significant risk for systems where the telnet service remains enabled and unpatched. Attackers can use this information to craft targeted brute force attacks against specific accounts, bypass account lockout mechanisms, or identify accounts that may have weak passwords. The vulnerability also enables attackers to determine whether specific domain accounts exist, potentially allowing for more sophisticated attack vectors such as credential stuffing or pass-the-hash attacks. This information disclosure can be particularly damaging in environments where the Guest account is enabled and accessible, as it provides attackers with a readily exploitable account with minimal privileges.
From a cybersecurity framework perspective, this vulnerability aligns with CWE-200, which describes the improper exposure of sensitive information, and maps to ATT&CK technique T1087.001 for account discovery through credential dumping and enumeration. The vulnerability demonstrates the importance of proper input validation and error handling in network services, as well as the necessity of implementing secure authentication protocols. Organizations should consider implementing network segmentation to limit access to telnet services, deploying intrusion detection systems to monitor for suspicious authentication patterns, and ensuring that telnet services are either disabled or replaced with more secure alternatives such as SSH. The vulnerability also highlights the importance of regular security assessments and vulnerability management programs to identify and remediate similar flaws in legacy systems that may still be operational in enterprise environments.