CVE-2015-5252 in Advanced Support Gateway
Summary
by MITRE
vfs.c in smbd in Samba 3.x and 4.x before 4.1.22, 4.2.x before 4.2.7, and 4.3.x before 4.3.3, when share names with certain substring relationships exist, allows remote attackers to bypass intended file-access restrictions via a symlink that points outside of a share.
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Analysis
by VulDB Data Team • 12/01/2022
The vulnerability described in CVE-2015-5252 represents a critical access control flaw within the Samba file sharing implementation that affects multiple versions of the Samba server software. This issue resides in the virtual file system component known as vfs.c within the smbd daemon, which serves as the core file sharing service in Samba installations. The vulnerability specifically manifests when multiple shares exist with overlapping or related substring names, creating a condition where maliciously crafted symlink references can escape the intended share boundaries and access files outside of their designated scope.
The technical exploitation of this vulnerability relies on the improper handling of symbolic links within the Samba file system traversal logic. When shares are configured with names that contain substrings of other share names, the path resolution mechanism fails to properly validate symlink targets against the share boundaries. This occurs because the Samba server does not adequately enforce access controls when processing symbolic links that point to locations outside the current share context. Attackers can leverage this by creating or manipulating symbolic links that reference files in other shares, effectively bypassing the intended access restrictions and gaining unauthorized access to sensitive data across different share boundaries.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass complete data exposure across multiple share configurations. An attacker who can successfully exploit this vulnerability gains the ability to traverse file system boundaries and access files that should be restricted to specific shares, potentially exposing confidential documents, system files, or user data. This issue particularly affects environments where multiple shares are configured with similar naming conventions, making it more prevalent in complex enterprise file sharing scenarios. The vulnerability can be exploited remotely without requiring authentication for the specific share being targeted, as the attack vector operates through the symlink manipulation within the broader Samba file system processing.
This vulnerability maps directly to CWE-22, which describes improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal attacks. The flaw demonstrates characteristics of CWE-284, which covers improper access control, as the vulnerability allows unauthorized access to resources beyond the intended share boundaries. From an ATT&CK framework perspective, this vulnerability aligns with T1078, which covers valid accounts and T1566, which covers malicious file execution, as attackers can leverage this to gain access to restricted files and potentially execute malicious code through compromised file access. The remediation strategy involves applying the official security patches released by Samba developers, specifically upgrading to versions 4.1.22, 4.2.7, or 4.3.3, which contain the necessary fixes to properly validate symlink targets against share boundaries. Additionally, system administrators should implement proper share naming conventions to minimize substring overlap and consider implementing additional access controls through firewall rules or network segmentation to limit exposure to this vulnerability.