CVE-2017-8563 in Windows
Summary
by MITRE
Microsoft Windows 7 SP1, Windows Server 2008 SP2 and R2 SP1, Windows 8.1 and Windows RT 8.1, Windows Server 2012 and R2, Windows 10 Gold, 1511, 1607, 1703, and Windows Server 2016 allows an elevation of privilege vulnerability due to Kerberos falling back to NT LAN Manager (NTLM) Authentication Protocol as the default authentication protocol, aka "Windows Elevation of Privilege Vulnerability".
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Analysis
by VulDB Data Team • 12/31/2020
The vulnerability identified as CVE-2017-8563 represents a critical elevation of privilege flaw within Microsoft Windows operating systems that affects multiple versions including Windows 7 SP1 through Windows 10 versions 1511, 1607, and 1703 along with their respective server counterparts. This security weakness stems from the Kerberos authentication protocol's default fallback behavior to the older NT LAN Manager authentication protocol when Kerberos authentication fails or is unavailable. The underlying technical mechanism involves the Windows authentication subsystem's inability to properly handle the transition between these two distinct authentication methods, creating a potential attack vector for malicious actors to escalate their privileges within the system.
The operational impact of this vulnerability extends beyond simple privilege escalation as it enables attackers to potentially gain unauthorized access to system resources and elevate their privileges from standard user level to administrative rights. This flaw particularly affects environments where Kerberos authentication is not properly configured or where network conditions cause Kerberos failures, forcing the system to automatically fall back to NTLM authentication which has known security weaknesses and vulnerabilities. The vulnerability aligns with CWE-287 which addresses improper authentication issues, specifically targeting weak authentication mechanisms that can be exploited to gain unauthorized access to system resources. Attackers can leverage this weakness by manipulating network conditions or authentication parameters to force the system into using NTLM authentication, thereby bypassing the more secure Kerberos protocol.
Security researchers have categorized this vulnerability under the MITRE ATT&CK framework as falling within the privilege escalation category, specifically targeting techniques that involve exploiting authentication mechanisms to gain higher system privileges. The flaw represents a significant concern for enterprise environments where Windows systems are deployed, as it can be exploited by attackers who may have already gained initial access to a system through other means. The vulnerability is particularly dangerous in domain environments where Kerberos authentication is expected to be the primary method of authentication, but network issues or misconfigurations can cause the system to fall back to NTLM which lacks the security features of Kerberos. Organizations may be vulnerable to attacks that exploit this behavior through man-in-the-middle attacks or network manipulation techniques that force authentication failures, thereby triggering the insecure fallback mechanism.
Mitigation strategies for CVE-2017-8563 primarily focus on enforcing proper Kerberos authentication configuration and disabling NTLM authentication where possible. System administrators should implement Group Policy settings to enforce Kerberos-only authentication and disable NTLM authentication entirely in environments where it is not required. The vulnerability can be addressed through Microsoft security updates that modify the authentication fallback behavior and strengthen the default authentication protocols. Organizations should also implement network monitoring solutions to detect unusual authentication patterns and ensure proper Kerberos configuration through tools like Kerberos Key Distribution Center validation. Additionally, implementing network segmentation and firewall rules can prevent attackers from manipulating authentication parameters to force the fallback to NTLM authentication, thereby reducing the attack surface for this specific vulnerability.