CVE-2016-2114 in Samba
Summary
by MITRE
The SMB1 protocol implementation in Samba 4.x before 4.2.11, 4.3.x before 4.3.8, and 4.4.x before 4.4.2 does not recognize the "server signing = mandatory" setting, which allows man-in-the-middle attackers to spoof SMB servers by modifying the client-server data stream.
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Analysis
by VulDB Data Team • 07/24/2022
The vulnerability identified as CVE-2016-2114 represents a critical weakness in the Samba implementation of the Server Message Block version 1 protocol that affected multiple versions of the Samba software family. This flaw specifically targets the authentication and data integrity mechanisms within the SMB1 protocol stack, creating a significant security gap that could be exploited by malicious actors positioned within network traffic streams. The vulnerability stems from Samba's failure to properly enforce the "server signing = mandatory" configuration setting, which is designed to ensure that all SMB communications are cryptographically signed to prevent tampering and impersonation attacks.
The technical root cause of this vulnerability lies in the improper handling of SMB1 protocol negotiations and signature validation within Samba's server implementation. When the "server signing = mandatory" parameter is configured, it should force all SMB communications to require cryptographic signatures that verify the authenticity of both client and server endpoints. However, Samba versions prior to the patched releases failed to enforce this mandatory signature requirement, allowing attackers to intercept and modify network traffic without detection. This weakness specifically impacts the SMB1 protocol's ability to maintain secure communication channels, as the system does not properly validate the integrity of data streams between client and server components.
The operational impact of CVE-2016-2114 is substantial, as it enables man-in-the-middle attacks that can successfully spoof legitimate SMB servers and manipulate data transmission. Attackers exploiting this vulnerability can modify client-server communications in real-time, potentially altering file transfers, authentication responses, or other SMB operations without either party detecting the interference. This capability significantly undermines the security posture of networks relying on Samba for file sharing and authentication services, particularly in environments where SMB1 remains enabled for backward compatibility reasons. The vulnerability affects organizations running affected Samba versions across multiple release branches, making it a widespread concern for enterprise network security.
From a cybersecurity perspective, this vulnerability aligns with CWE-310, which addresses cryptographic weaknesses in authentication systems, and maps to ATT&CK technique T1071.004 for application layer protocol usage. The exploitation of this vulnerability requires minimal privileges and can be performed by attackers with network access, making it particularly dangerous in shared or untrusted network environments. Organizations should consider implementing immediate mitigations including disabling SMB1 protocol support, enforcing mandatory signing requirements, and deploying network monitoring solutions to detect potential exploitation attempts. The vulnerability also highlights the importance of proper protocol implementation validation and the need for comprehensive security testing of authentication mechanisms, particularly in widely deployed open source software components that serve as critical infrastructure elements for enterprise file sharing and network authentication services.