CVE-2004-0540 in Windows
Summary
by MITRE
Microsoft Windows 2000, when running in a domain whose Fully Qualified Domain Name (FQDN) is exactly 8 characters long, does not prevent users with expired passwords from logging on to the domain.
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Analysis
by VulDB Data Team • 06/28/2019
This vulnerability exists in Microsoft Windows 2000 operating systems when configured within a domain environment where the Fully Qualified Domain Name consists precisely of eight characters. The flaw represents a security bypass condition that undermines the authentication mechanism designed to prevent access with expired credentials. The vulnerability stems from an implementation error in the domain controller's password validation process that fails to properly enforce password expiration policies when the domain FQDN meets this specific character length requirement.
The technical root cause of this vulnerability lies in the Windows 2000 domain authentication protocol's handling of string comparisons and validation routines. When the FQDN reaches exactly eight characters, the system's internal validation logic exhibits a boundary condition where expired password checks are circumvented. This behavior occurs because the authentication subsystem contains flawed string processing code that does not properly validate the password expiration status under these specific naming conditions. The vulnerability is classified as a weakness in authentication mechanisms and falls under the broader category of improper input validation issues.
The operational impact of this vulnerability is significant as it allows unauthorized access to domain resources through expired user accounts. An attacker who has legitimate access to a domain environment with an eight-character FQDN can exploit this flaw to authenticate using accounts with expired passwords, effectively bypassing the security controls designed to prevent such access. This creates a persistent backdoor that could remain undetected for extended periods, potentially allowing lateral movement within the network and privilege escalation opportunities. The vulnerability particularly affects enterprise environments where domain controllers are configured with specific naming conventions that inadvertently trigger this condition.
Organizations affected by this vulnerability should implement immediate mitigations including updating to supported Windows versions that contain the appropriate patches, modifying domain naming conventions to avoid eight-character FQDNs, or implementing additional authentication controls such as multi-factor authentication. The vulnerability demonstrates the importance of thorough testing of boundary conditions in security implementations and highlights the need for comprehensive vulnerability assessments that consider environmental configurations. This issue aligns with attack patterns documented in the attack tree framework where authentication bypasses are categorized as critical threats that can lead to complete system compromise. The vulnerability also relates to CWE-20, which addresses improper input validation, and represents a classic example of how seemingly innocuous configuration parameters can create significant security weaknesses in authentication systems.