CVE-2018-1139 in Samba
Summary
by MITRE
A flaw was found in the way samba before 4.7.9 and 4.8.4 allowed the use of weak NTLMv1 authentication even when NTLMv1 was explicitly disabled. A man-in-the-middle attacker could use this flaw to read the credential and other details passed between the samba server and client.
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Analysis
by VulDB Data Team • 05/04/2023
The vulnerability identified as CVE-2018-1139 represents a critical authentication weakness in samba implementations prior to versions 4.7.9 and 4.8.4. This flaw operates at the core of network authentication protocols where samba servers fail to properly enforce security policies regarding NTLM authentication methods. The issue stems from samba's handling of authentication requests where it permits the use of weak NTLMv1 credentials even when administrators have explicitly configured the system to disable such authentication mechanisms. This represents a fundamental failure in access control enforcement and policy adherence within the samba service implementation.
The technical nature of this vulnerability aligns with CWE-327, which addresses the use of weak cryptographic algorithms, and CWE-287, which covers improper authentication handling. The flaw specifically manifests when samba servers receive authentication requests from clients that have been configured to use NTLMv1 despite explicit configuration to disable it. This occurs through the protocol negotiation process where samba servers fail to properly validate that the authentication method being used aligns with the configured security policies. The vulnerability creates a path where an attacker can exploit the inconsistent enforcement of authentication policies to downgrade security measures.
From an operational perspective, this vulnerability creates significant risk for organizations relying on samba for file sharing and network authentication services. A man-in-the-middle attacker positioned between samba clients and servers can intercept authentication traffic and leverage the weak NTLMv1 authentication to obtain user credentials and other sensitive information. The impact extends beyond simple credential theft to potentially provide attackers with unauthorized access to network resources, file systems, and other services protected by the compromised samba authentication. This vulnerability particularly affects environments where samba is used for domain authentication, file sharing, or printer services where credential exposure could lead to broader network compromise.
The security implications of CVE-2018-1139 align with several ATT&CK techniques including T1075, which covers the use of legitimate credentials for access, and T1550, which covers use of valid accounts for lateral movement. Organizations implementing samba services should prioritize immediate patching to versions 4.7.9 or 4.8.4, as these releases contain the necessary fixes to properly enforce NTLM authentication policies. Additional mitigations include configuring samba to explicitly disable NTLMv1 authentication through appropriate configuration parameters, implementing network monitoring to detect anomalous authentication patterns, and conducting security assessments to verify that authentication policies are properly enforced. The vulnerability demonstrates the critical importance of proper authentication policy enforcement and the potential consequences of protocol downgrade attacks in network security environments.