CVE-2005-3173 in Windows
Summary
by MITRE
microsoft windows 2000 before update rollup 1 for sp4 does not apply group policies if the user logs on using upn credentials with a trailing dot which prevents windows 2000 from finding the correct domain controller and could allow the user to bypass intended restrictions.
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Analysis
by VulDB Data Team • 07/06/2021
This vulnerability affects Microsoft Windows 2000 systems prior to Update Rollup 1 for Service Pack 4 and relates to improper handling of User Principal Name (UPN) credentials during user authentication processes. The flaw specifically manifests when users authenticate using UPN formats that contain trailing dots, which creates a condition where the operating system cannot correctly resolve the domain controller for group policy application. This issue stems from the Windows authentication subsystem's inability to properly normalize or validate UPN strings before attempting domain controller discovery and group policy processing. The vulnerability represents a significant security concern as it allows authenticated users to bypass intended access controls and restrictions that would normally be enforced through group policy objects. From a technical perspective, this issue falls under the category of authentication bypass mechanisms and relates to improper input validation within the Windows security framework.
The operational impact of this vulnerability extends beyond simple authentication failures to encompass broader security policy enforcement mechanisms. When a user logs on with a UPN containing a trailing dot, the Windows 2000 authentication process fails to properly resolve the domain controller, resulting in group policy application being skipped or incorrectly applied. This condition creates a potential security gap where users may inherit default or less restrictive policies instead of the intended restricted policies. The vulnerability is particularly concerning in enterprise environments where group policies are used to enforce security configurations, access controls, and compliance requirements. Attackers could potentially exploit this weakness to gain elevated privileges or access to restricted resources by manipulating their UPN credentials to include trailing dots, effectively bypassing security controls that should be enforced through group policy mechanisms.
This vulnerability aligns with several cybersecurity frameworks and threat modeling approaches, including CWE-20, which addresses "Improper Input Validation," and relates to ATT&CK technique T1550.001 for "Use of Valid Credentials" where attackers leverage legitimate authentication mechanisms to bypass security controls. The issue demonstrates how seemingly minor input formatting inconsistencies can create significant security implications in enterprise authentication systems. Organizations running Windows 2000 systems without the appropriate update rollup are particularly vulnerable to this type of credential manipulation attack. The flaw exposes a gap in the Windows 2000 security model where the system fails to properly validate authentication credentials before proceeding with domain controller resolution and policy application processes. This represents a failure in the principle of least privilege enforcement and could potentially allow attackers to circumvent security controls that are critical for maintaining enterprise security posture.
The recommended mitigation strategy involves applying Update Rollup 1 for Windows 2000 Service Pack 4, which addresses the specific UPN validation issue. Organizations should also implement monitoring solutions to detect unusual authentication patterns or credential formats that might indicate exploitation attempts. Additionally, security administrators should review and audit existing UPN naming conventions to ensure they do not inadvertently introduce trailing dots or other malformed characters. System hardening measures should include implementing proper credential validation policies and ensuring that authentication systems properly normalize input before processing. The vulnerability serves as a reminder of the importance of thorough input validation in security-critical systems and highlights how legacy operating systems may contain unpatched vulnerabilities that could be exploited in enterprise environments. Organizations should also consider implementing additional authentication controls and monitoring mechanisms to detect and prevent exploitation attempts targeting this specific weakness in the Windows 2000 authentication framework.