CVE-2025-21311 in Windows
Summary
by MITRE • 01/14/2025
Windows NTLM V1 Elevation of Privilege Vulnerability
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Analysis
by VulDB Data Team • 05/09/2026
This vulnerability involves a critical security flaw in the Windows NTLM authentication protocol that allows attackers to escalate privileges through weak authentication mechanisms. The vulnerability specifically affects systems that accept NTLMv1 authentication, which is considered fundamentally insecure due to its cryptographic weaknesses and susceptibility to various attack vectors including credential theft and relay attacks. The flaw stems from the inherent design limitations of the NTLMv1 protocol where the authentication process does not adequately protect against man-in-the-middle attacks or credential replay scenarios.
The technical implementation of this vulnerability occurs when systems configured to accept NTLMv1 authentication receive authentication requests that can be manipulated by attackers to gain unauthorized access. This typically happens in environments where legacy applications or services still rely on NTLMv1 authentication methods, or when security policies have not been properly configured to disable weak authentication protocols. The vulnerability is particularly dangerous because NTLMv1 uses a weak hashing algorithm that can be cracked using rainbow table attacks or brute force methods, allowing attackers to obtain valid credentials that can then be used to escalate privileges within the network.
From an operational impact perspective, this vulnerability enables attackers to move laterally within networks and gain elevated privileges on target systems. The attack chain typically begins with credential harvesting through techniques such as SMB relay attacks or network sniffing, followed by privilege escalation once valid credentials are obtained. Organizations may experience significant security breaches where attackers can access sensitive data, modify system configurations, or establish persistent access points within the network infrastructure. The vulnerability is particularly concerning in enterprise environments where multiple systems may be configured to accept NTLMv1 authentication without proper security controls.
Security mitigation strategies should focus on disabling NTLMv1 authentication entirely and enforcing stronger authentication mechanisms such as NTLMv2 or Kerberos. Network administrators should implement proper security policies that prevent NTLMv1 authentication and configure systems to require more secure authentication protocols. The implementation of security controls such as SMB signing, secure authentication policies, and network segmentation can significantly reduce the attack surface. Organizations should also conduct regular security assessments to identify systems that may still be accepting NTLMv1 authentication and ensure that all network services have been properly configured to reject weak authentication methods. This vulnerability aligns with CWE-256 and CWE-310 categories related to weak cryptographic algorithms and authentication mechanisms, and represents a significant concern in the ATT&CK framework under privilege escalation and credential access tactics.
The remediation process requires comprehensive network-wide assessment to identify all systems accepting NTLMv1 authentication, followed by implementation of Group Policy settings that disable the protocol. Security teams should also implement monitoring solutions that can detect attempts to use NTLMv1 authentication and alert administrators to potential exploitation attempts. Regular vulnerability scanning and penetration testing should be conducted to ensure that no systems remain vulnerable to this attack vector. The vulnerability demonstrates the critical importance of maintaining up-to-date security configurations and the dangers of legacy authentication protocols that have known cryptographic weaknesses.