CVE-2015-6095 in Windows
Summary
by MITRE
Kerberos in Microsoft Windows Vista SP2, Windows Server 2008 SP2 and R2 SP1, Windows 7 SP1, Windows 8, Windows 8.1, Windows Server 2012 Gold and R2, Windows RT Gold and 8.1, and Windows 10 Gold and 1511 mishandles password changes, which allows physically proximate attackers to bypass authentication, and conduct decryption attacks against certain BitLocker configurations, by connecting to an unintended Key Distribution Center (KDC), aka "Windows Kerberos Security Feature Bypass."
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Analysis
by VulDB Data Team • 11/18/2024
This vulnerability represents a critical security flaw in Microsoft Windows Kerberos authentication implementation that affects multiple operating system versions including Vista SP2 through Windows 10 version 1511. The issue stems from improper handling of password changes within the Kerberos protocol framework, creating a significant authentication bypass opportunity for attackers who can physically access target systems. The vulnerability specifically manifests when users change their passwords, allowing malicious actors to exploit the authentication flow to gain unauthorized access to systems protected by BitLocker encryption.
The technical root cause involves the Kerberos Key Distribution Center (KDC) not properly validating or handling password change requests during the authentication process. When users modify their passwords, the system should ensure that subsequent authentication attempts use the updated credentials and that the KDC properly validates these changes. However, the flaw allows attackers to connect to an unintended KDC instance, effectively bypassing the normal authentication mechanisms that should enforce password updates. This misconfiguration enables attackers to maintain access to systems even after password changes have been implemented, particularly affecting BitLocker-encrypted volumes that rely on proper Kerberos authentication for decryption operations.
The operational impact of this vulnerability extends beyond simple authentication bypass to include serious data confidentiality risks, especially for systems utilizing BitLocker encryption. Attackers can exploit this weakness to perform decryption attacks against BitLocker configurations, potentially gaining access to encrypted data without proper authorization. The vulnerability's proximity requirement means that attackers must be physically near target systems to exploit it, but this limitation does not mitigate the severity of potential damage. Organizations with systems running affected Windows versions face significant risk of unauthorized data access, particularly in environments where physical security controls may be inadequate.
This vulnerability aligns with CWE-287, which addresses improper authentication issues in authentication systems, and maps to ATT&CK technique T1078 for valid accounts and T1552 for credentials from password files. The security implications extend to enterprise environments where Kerberos authentication is extensively used for single sign-on capabilities and system access control. Organizations should prioritize immediate patch deployment for all affected Windows versions, particularly focusing on systems containing sensitive data protected by BitLocker encryption. Additional mitigations include implementing network segmentation to limit access to KDC services, enabling enhanced monitoring for unusual authentication patterns, and ensuring proper physical security controls around critical systems. The vulnerability highlights the importance of proper authentication flow management and demonstrates how seemingly minor implementation flaws in core security protocols can create significant exploitation opportunities for determined attackers.