CVE-2016-2118 in Samba
Summary
by MITRE
The MS-SAMR and MS-LSAD protocol implementations in Samba 3.x and 4.x before 4.2.11, 4.3.x before 4.3.8, and 4.4.x before 4.4.2 mishandle DCERPC connections, which allows man-in-the-middle attackers to perform protocol-downgrade attacks and impersonate users by modifying the client-server data stream, aka "BADLOCK."
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Analysis
by VulDB Data Team • 01/27/2025
The vulnerability identified as CVE-2016-2118 represents a critical security flaw in the Samba implementation of Microsoft's Server Message Block (SMB) protocol suite, specifically affecting the MS-SAMR and MS-LSAD protocol layers. This vulnerability resides in the Distributed Computing Environment/Remote Procedure Call (DCE/RPC) connection handling mechanisms within Samba versions 3.x and 4.x prior to the specified patched releases. The flaw enables attackers to perform sophisticated man-in-the-middle attacks by manipulating the communication stream between client and server components, fundamentally undermining the security assurances typically provided by these network protocols.
The technical implementation of this vulnerability stems from improper handling of DCE/RPC connections within the Samba authentication framework, particularly during the negotiation phase of the authentication process. When a client attempts to establish a connection with a Samba server using these protocols, the vulnerable implementation fails to properly validate the integrity of the communication channel. This weakness creates a window of opportunity for attackers to perform protocol-downgrade attacks, where they can force the connection to use less secure authentication mechanisms. The vulnerability is classified as CWE-290 due to its nature as a credential management flaw that allows for authentication bypass through protocol manipulation.
The operational impact of CVE-2016-2118 is severe and far-reaching, as it enables attackers to impersonate legitimate users within the network environment. This capability allows for unauthorized access to sensitive resources, privilege escalation, and potential lateral movement throughout the network infrastructure. The vulnerability specifically affects Windows domain controllers and servers running Samba, making it particularly dangerous in enterprise environments where these systems serve as critical authentication points. The attack vector requires only network access to the target system, making it relatively easy to exploit in environments where network segmentation is insufficient or non-existent.
Security practitioners should implement immediate mitigations including updating Samba to versions 4.2.11, 4.3.8, or 4.4.2, depending on their current deployment. Network segmentation and firewall rules should be enforced to restrict access to Samba services, particularly on ports 139 and 445. The vulnerability aligns with ATT&CK technique T1075 which covers the use of legitimate credentials for unauthorized access, and T1557 which addresses credential harvesting through man-in-the-middle attacks. Organizations should also consider implementing network monitoring solutions capable of detecting anomalous DCE/RPC traffic patterns that might indicate exploitation attempts. The vulnerability demonstrates the critical importance of maintaining up-to-date software implementations and proper network security controls to prevent protocol-level attacks that can compromise entire authentication infrastructures.