CVE-2016-3237 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; Windows RT 8.1; and Windows 10 Gold, 1511, and 1607 allows man-in-the-middle attackers to bypass authentication via vectors related to a fallback to NTLM authentication during a domain account password change, aka "Kerberos Security Feature Bypass Vulnerability."
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Analysis
by VulDB Data Team • 05/10/2025
The vulnerability identified as CVE-2016-3237 represents a critical security flaw in Microsoft Windows Kerberos authentication implementations across multiple operating system versions including Windows Vista SP2 through Windows 10 version 1607. This vulnerability specifically targets the Kerberos authentication protocol's handling of domain account password changes and creates a pathway for man-in-the-middle attacks to bypass authentication mechanisms. The flaw operates through a fallback mechanism that automatically switches from Kerberos to NTLM authentication during password change operations, creating an exploitable condition that undermines the security assurances typically provided by Kerberos.
The technical implementation of this vulnerability stems from how Windows handles authentication fallback scenarios when Kerberos authentication fails or is unavailable. During domain account password changes, the system is designed to fall back to NTLM authentication as a secondary mechanism, but this fallback process contains a critical flaw that allows attackers to intercept and manipulate the authentication flow. The vulnerability specifically affects the Kerberos authentication process when it encounters conditions that trigger the fallback to NTLM, creating an authentication bypass scenario where malicious actors can authenticate without proper credentials. This behavior violates the fundamental security principle that authentication mechanisms should maintain strong cryptographic assurances throughout the entire authentication process.
From an operational impact perspective, this vulnerability enables attackers to perform unauthorized authentication against domain accounts by exploiting the fallback mechanism during password change operations. The attack vector specifically targets the transition period between Kerberos and NTLM authentication, allowing adversaries to intercept network traffic and manipulate the authentication flow to gain access to systems and resources that should require proper authentication. The vulnerability is particularly concerning because it affects a core Windows authentication mechanism that is widely deployed across enterprise environments, potentially enabling attackers to escalate privileges, access sensitive data, and move laterally within networks. The security implications extend beyond simple credential theft, as successful exploitation can lead to complete domain compromise and persistent access to enterprise resources.
Mitigation strategies for CVE-2016-3237 should focus on implementing immediate patches from Microsoft as well as network-level protections to prevent man-in-the-middle attacks during authentication processes. Organizations should ensure that all affected Windows systems receive the relevant security updates, particularly the Windows 10 updates for versions 1511 and 1607, which addressed this specific vulnerability. Network administrators should consider implementing additional authentication security measures such as enforcing strong encryption requirements, monitoring authentication traffic for suspicious patterns, and ensuring that Kerberos authentication is properly configured to avoid unnecessary fallback scenarios. The vulnerability aligns with CWE-305, which addresses authentication bypass issues, and represents a specific instance of the broader ATT&CK technique T1550.003, which covers the use of Kerberos authentication to gain access to systems. Organizations should also consider implementing network segmentation and monitoring solutions to detect and prevent exploitation attempts, as the vulnerability specifically targets the authentication process during password change operations where network traffic is most vulnerable to interception and manipulation.