CVE-2003-0904 in Exchange
Summary
by MITRE
Microsoft Exchange 2003 and Outlook Web Access (OWA), when configured to use NTLM authentication, does not properly reuse HTTP connections, which can cause OWA users to view mailboxes of other users when Kerberos has been disabled as an authentication method for IIS 6.0, e.g. when SharePoint Services 2.0 is installed.
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Analysis
by VulDB Data Team • 07/20/2025
This vulnerability exists in Microsoft Exchange Server 2003 and Outlook Web Access (OWA) implementations that utilize NTLM authentication mechanisms. The core issue stems from improper HTTP connection handling within the web server infrastructure, specifically when Kerberos authentication is disabled for IIS 6.0. When SharePoint Services 2.0 is installed, it typically disables Kerberos authentication as part of its configuration, creating an environment where NTLM authentication becomes the primary method for user authentication. The flaw manifests when the HTTP connection management system fails to properly reset authentication state between different user sessions, allowing session reuse across multiple user contexts. This misconfiguration creates a critical security gap where authenticated users can potentially access mailbox data belonging to other users within the same Exchange organization. The vulnerability directly relates to CWE-284, which addresses improper access control mechanisms, and aligns with ATT&CK technique T1078 for valid accounts and T1566 for credential access through exploitation of authentication mechanisms. The technical implementation issue occurs at the HTTP protocol level where connection pooling does not adequately separate authentication contexts, causing authentication tokens to persist across user sessions. This behavior violates fundamental security principles of isolation and access control, as the system fails to properly enforce user boundaries during web session management.
The operational impact of this vulnerability extends beyond simple information disclosure, as it creates a persistent risk for organizations using Exchange 2003 with OWA and SharePoint integration. Attackers who gain initial access through any means can exploit this flaw to escalate privileges and access sensitive email communications, calendar data, and contact information belonging to other users within the same domain. The vulnerability is particularly concerning because it operates silently without generating obvious audit trail indicators, making detection difficult. Organizations with multiple users accessing OWA simultaneously face increased risk, as the connection reuse behavior can occur unpredictably across different user sessions. The flaw becomes more pronounced in environments where SharePoint Services 2.0 is deployed, as this configuration typically disables Kerberos authentication by default, forcing the system to rely on NTLM authentication mechanisms that exhibit this problematic behavior. This creates a cascading security risk where the presence of one service (SharePoint) inadvertently introduces vulnerabilities in another service (Exchange OWA). The vulnerability essentially creates a backdoor mechanism for privilege escalation and data exfiltration, as legitimate users can access unauthorized mailbox contents through normal web browsing activities.
Mitigation strategies for this vulnerability require a multi-layered approach focusing on both configuration changes and architectural considerations. The primary recommendation involves enabling Kerberos authentication for IIS 6.0 when using Exchange 2003 with OWA, which eliminates the problematic NTLM connection reuse behavior. Organizations should also implement proper connection management policies that enforce strict session isolation and disable HTTP connection pooling for authentication-critical applications. Network-level security controls including firewall rules and intrusion detection systems can help monitor for unusual authentication patterns or cross-user access attempts. Additionally, implementing regular security auditing and monitoring of IIS logs can help detect anomalous behavior indicative of exploitation attempts. System administrators should consider upgrading to newer Exchange Server versions that have addressed this specific connection management flaw, as Exchange 2003 reached end-of-life and no longer receives security updates. The vulnerability demonstrates the importance of understanding inter-service dependencies and authentication method conflicts within enterprise environments, particularly when integrating web applications like SharePoint with email systems such as Exchange. Organizations should also implement role-based access controls and least privilege principles to minimize the impact of successful exploitation attempts, ensuring that even if an attacker can access other users' mailboxes, they cannot access all system resources. Regular security assessments should evaluate the interaction between authentication methods and connection management behaviors across all integrated applications to prevent similar vulnerabilities from emerging in other system components.