CVE-2001-0660 in Exchange
Summary
by MITRE
Outlook Web Access (OWA) in Microsoft Exchange 5.5, SP4 and earlier, allows remote attackers to identify valid user email addresses by directly accessing a back-end function that processes the global address list (GAL).
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Analysis
by VulDB Data Team • 10/05/2025
This vulnerability exists in Microsoft Exchange Server 5.5 with Service Pack 4 and earlier versions where Outlook Web Access functionality contains a back-end component that processes global address list requests without proper authentication validation. The flaw allows remote attackers to directly access internal functions that would normally require valid user credentials or session tokens to access. When an attacker sends a specially crafted request to the OWA interface, the system processes the global address list query without verifying the legitimacy of the requester, thereby exposing valid email addresses from the organization's directory. This represents a classic information disclosure vulnerability that violates fundamental security principles of access control and authentication enforcement. The vulnerability is classified under CWE-200, which deals with information exposure, and specifically relates to insufficient authentication mechanisms within web applications. The attack vector is particularly concerning because it operates over standard network protocols without requiring any prior authentication credentials, making it accessible to anyone with network access to the Exchange server.
The technical implementation of this vulnerability stems from improper input validation and access control enforcement within the Exchange Web server components. The global address list processing function does not perform adequate verification of incoming requests, allowing attackers to bypass normal authentication procedures that would typically be required to access directory services. This weakness enables attackers to enumerate valid email addresses through systematic probing of the affected interface, potentially building comprehensive lists of users within the organization. The operational impact extends beyond simple information disclosure as this data can be used for subsequent social engineering attacks, credential stuffing attempts, or targeted phishing campaigns. Attackers can leverage the discovered email addresses to conduct more sophisticated attacks by using them in password spraying or brute force attacks against the identified accounts. This vulnerability directly aligns with tactics described in the MITRE ATT&CK framework under the reconnaissance phase where adversaries gather information about target systems and users to plan more effective attacks.
Organizations affected by this vulnerability face significant operational risks including potential insider threat exposure and increased attack surface for subsequent compromise attempts. The disclosure of valid email addresses provides attackers with a valuable asset for planning targeted attacks against specific individuals within the organization. Security professionals should note that this vulnerability demonstrates the critical importance of proper access control implementation even for internal functions that are not directly exposed to end users. The remediation strategy involves implementing proper authentication checks for all backend functions that process directory queries and ensuring that all access to sensitive organizational data requires valid credentials. Microsoft addressed this vulnerability through service pack updates and security patches that enforced proper authentication mechanisms for global address list access. Organizations should implement network segmentation to limit access to Exchange servers, deploy proper firewall rules to restrict access to OWA interfaces, and regularly audit their web application security configurations to prevent similar vulnerabilities from being introduced in future deployments. The incident highlights the necessity of thorough security testing of web applications, particularly those handling sensitive organizational data, and the importance of following secure coding practices that enforce proper authentication and authorization checks at all levels of application architecture.