CVE-2016-0049 in Windows
Summary
by MITRE
Kerberos in Microsoft Windows Vista SP2, Windows Server 2008 SP2 and R2 SP1, Windows 7 SP1, Windows 8.1, Windows Server 2012 Gold and R2, and Windows 10 Gold and 1511 does not properly validate password changes, which allows remote attackers to bypass authentication by deploying a crafted Key Distribution Center (KDC) and then performing a sign-in action, aka "Windows Kerberos Security Feature Bypass."
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Analysis
by VulDB Data Team • 05/04/2025
This vulnerability represents a critical security flaw in Microsoft Windows Kerberos authentication systems that affects multiple operating system versions including Windows Vista SP2 through Windows 10 1511. The vulnerability stems from insufficient validation of password changes within the Kerberos protocol implementation, creating a pathway for remote attackers to bypass authentication mechanisms through malicious KDC deployment. The flaw specifically impacts the Windows Kerberos security feature, allowing unauthorized access through crafted authentication requests that exploit weaknesses in the password change validation process. This vulnerability operates at the core of Windows authentication infrastructure and represents a significant bypass of security controls that should prevent unauthorized system access.
The technical implementation of this vulnerability occurs when a malicious actor deploys a crafted Key Distribution Center that can manipulate the Kerberos authentication flow during password change operations. The flaw allows attackers to perform sign-in actions without proper authentication by exploiting how the system validates password modifications. This bypass occurs because the Windows Kerberos implementation fails to properly validate the authenticity and integrity of password change requests, enabling attackers to impersonate legitimate users. The vulnerability operates through the Kerberos protocol's ticket-granting service and key distribution mechanisms, where the system should validate that password changes originate from legitimate sources but instead accepts maliciously crafted requests. This represents a failure in the Kerberos protocol's integrity validation mechanisms that aligns with CWE-287, which addresses improper authentication issues in authentication systems.
The operational impact of this vulnerability extends beyond simple unauthorized access to encompass potential full system compromise and lateral movement within networks. Attackers can leverage this bypass to gain access to network resources, escalate privileges, and potentially establish persistent access points within targeted environments. The vulnerability is particularly dangerous in enterprise environments where Kerberos is commonly used for authentication, as it can enable attackers to move laterally across systems without detection. The attack requires remote access and the ability to deploy malicious KDC services, but once successful, provides attackers with legitimate authentication credentials that can bypass traditional security controls. This vulnerability creates a persistent threat vector that can be exploited repeatedly, as the bypass remains effective until the underlying Windows Kerberos implementation is patched.
Mitigation strategies for this vulnerability require immediate patch deployment from Microsoft, as the primary fix involves updating the Windows Kerberos implementation to properly validate password changes and authentication requests. Organizations should implement network segmentation and monitoring to detect unauthorized KDC deployments, as the vulnerability requires attackers to establish malicious KDC services within the network. Security teams should also review Kerberos authentication logs and implement anomaly detection for unusual authentication patterns that may indicate exploitation attempts. Additional protective measures include disabling unnecessary Kerberos services, implementing strict network access controls, and monitoring for unauthorized changes to authentication infrastructure. The mitigation approach aligns with ATT&CK technique T1550.003 for Kerberos, which addresses the exploitation of Kerberos authentication mechanisms and emphasizes the need for proper authentication validation controls. Organizations must also consider implementing multi-factor authentication and privilege separation to reduce the impact of successful exploitation attempts, as this vulnerability effectively allows attackers to bypass primary authentication controls and gain system access with legitimate credentials.