CVE-2016-2115 in Samba
Summary
by MITRE
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 does not require SMB signing within a DCERPC session over ncacn_np, which allows man-in-the-middle attackers to spoof SMB clients by modifying the client-server data stream.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 07/24/2022
The vulnerability identified as CVE-2016-2115 represents a critical security flaw in Samba implementations across multiple versions including 3.x and 4.x releases prior to specific patch levels. This vulnerability specifically affects the Distributed Computing Environment/Remote Procedure Call (DCE/RPC) functionality when operating over the ncacn_np transport protocol, which is commonly used for Windows RPC communication. The flaw stems from the absence of mandatory SMB signing requirements within DCERPC sessions, creating a significant attack vector for malicious actors.
The technical nature of this vulnerability resides in the lack of cryptographic integrity protection for data transmitted between SMB clients and servers within DCERPC sessions. When SMB signing is not enforced, attackers can exploit this weakness to perform man-in-the-middle attacks by intercepting and modifying the client-server communication stream. This modification allows adversaries to spoof legitimate SMB clients and potentially gain unauthorized access to network resources. The vulnerability operates at the transport layer of the SMB protocol stack, specifically targeting the authentication and session management mechanisms that should normally ensure data integrity and client authenticity.
The operational impact of CVE-2016-2115 extends beyond simple data interception, as it enables sophisticated attack scenarios that can compromise entire network infrastructures. Attackers leveraging this vulnerability can manipulate RPC calls to perform unauthorized operations, potentially escalating privileges or accessing sensitive network resources. The vulnerability is particularly dangerous in domain controller environments where Samba servers may be handling critical authentication and authorization functions. This flaw aligns with CWE-310, which addresses cryptographic weaknesses in authentication protocols, and represents a significant deviation from secure communication practices. Organizations running affected Samba versions face increased risk of credential theft, privilege escalation, and unauthorized network access.
Mitigation strategies for this vulnerability require immediate patching of all affected Samba installations to versions that properly enforce SMB signing requirements. System administrators should configure Samba servers to mandate SMB signing for all DCERPC sessions, particularly those operating over ncacn_np transport. Network segmentation and monitoring solutions should be implemented to detect anomalous RPC traffic patterns that might indicate exploitation attempts. The vulnerability demonstrates the importance of cryptographic integrity protection in distributed computing environments and aligns with ATT&CK technique T1075 which covers the use of valid accounts for unauthorized access. Organizations should also consider implementing additional security controls such as network access control lists and intrusion detection systems to provide defense-in-depth against potential exploitation attempts.