CVE-2015-7560 in Samba
Summary
by MITRE
The SMB1 implementation in smbd in Samba 3.x and 4.x before 4.1.23, 4.2.x before 4.2.9, 4.3.x before 4.3.6, and 4.4.x before 4.4.0rc4 allows remote authenticated users to modify arbitrary ACLs by using a UNIX SMB1 call to create a symlink, and then using a non-UNIX SMB1 call to write to the ACL content.
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Analysis
by VulDB Data Team • 07/10/2022
The vulnerability described in CVE-2015-7560 represents a critical access control flaw within the Server Message Block protocol implementation in Samba software versions spanning multiple release lines. This issue affects both Samba 3.x and 4.x branches, with specific versions requiring patching to address the security weakness. The vulnerability operates through a sophisticated attack vector that leverages the differences between UNIX and non-UNIX SMB1 protocol implementations to bypass normal access controls and manipulate file permissions.
The technical exploitation mechanism involves a multi-step process that begins with an authenticated user creating a symbolic link using a UNIX SMB1 call, which is then followed by a subsequent non-UNIX SMB1 call to write to the Access Control List content. This approach exploits the inconsistent handling of file operations between different SMB protocol variants within the same Samba implementation. The flaw resides in the improper validation of access controls during cross-protocol operations, allowing attackers to manipulate file permissions without proper authorization. This vulnerability specifically targets the SMB1 protocol implementation in smbd, which serves as the core file sharing daemon for Samba installations.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it enables attackers to modify arbitrary Access Control Lists on shared files and directories. This capability allows malicious users to potentially grant themselves or others unauthorized access to sensitive resources, effectively undermining the entire file sharing security model. The vulnerability is particularly dangerous in enterprise environments where Samba servers typically host critical data and where multiple users access shared resources through SMB protocols. Attackers can leverage this weakness to establish persistent access to network resources, potentially leading to data exfiltration, system compromise, or further lateral movement within the network infrastructure.
Security practitioners should recognize this vulnerability as a classic example of improper access control implementation, aligning with CWE-284 which addresses inadequate access control mechanisms. The attack pattern follows principles consistent with ATT&CK technique T1078 which covers valid accounts and privilege escalation through legitimate system access. Organizations running affected Samba versions should prioritize immediate patching across all systems, particularly those serving as file servers or domain controllers. Additional mitigations include implementing network segmentation, disabling SMB1 protocol where possible, and monitoring for unusual file access patterns that might indicate exploitation attempts. The vulnerability demonstrates the importance of consistent security controls across all protocol implementations within a single software stack, as inconsistencies between different protocol variants can create exploitable gaps in access control enforcement.