CVE-2017-2619 in Samba
Summary
by MITRE
Samba before versions 4.6.1, 4.5.7 and 4.4.11 are vulnerable to a malicious client using a symlink race to allow access to areas of the server file system not exported under the share definition.
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Analysis
by VulDB Data Team • 06/25/2025
The vulnerability described in CVE-2017-2619 represents a critical symlink race condition affecting Samba file servers across multiple version branches. This flaw allows malicious clients to exploit a timing window during file system operations to gain unauthorized access to directories and files that should be restricted by share definitions. The vulnerability stems from improper handling of symbolic links within Samba's file access control mechanisms, creating a window where a client can manipulate symlink references to bypass normal access controls. The issue is particularly concerning because it operates at the core of Samba's file system interaction model, potentially enabling attackers to access sensitive data that should remain protected within the server's file structure.
The technical implementation of this vulnerability involves a race condition between the server's symlink resolution and the client's file access operations. When a client attempts to access a file through a Samba share, the server performs symlink resolution to determine the actual file location. However, if an attacker can manipulate the symlink reference between the time the server checks the symlink and when it performs the actual file access, they can redirect the access to unintended locations. This race condition occurs because Samba does not properly synchronize access to symbolic links during the file resolution process, allowing malicious clients to substitute their own symlinks for legitimate ones. The flaw is categorized under CWE-367, which specifically addresses Time-of-Check to Time-of-Use (TOCTOU) vulnerabilities, where the state of a resource changes between the time it is checked and the time it is accessed.
The operational impact of this vulnerability extends far beyond simple unauthorized file access, as it can enable attackers to escalate privileges and gain access to sensitive system information. An attacker exploiting this vulnerability could potentially access system configuration files, user data, or even administrative directories that should be restricted to authorized users only. The vulnerability affects Samba versions 4.6.0 and earlier, 4.5.6 and earlier, and 4.4.10 and earlier, representing a significant portion of the Samba user base that was vulnerable to this attack vector. This type of vulnerability aligns with ATT&CK technique T1078 which covers valid accounts and privilege escalation, as attackers can leverage this flaw to access restricted resources without proper authentication. The impact is particularly severe in environments where Samba servers handle sensitive corporate data or serve as file shares for multiple users with varying access levels.
Mitigation strategies for CVE-2017-2619 focus primarily on upgrading to patched versions of Samba where the symlink race condition has been addressed through proper synchronization mechanisms. Organizations should immediately deploy Samba versions 4.6.1, 4.5.7, or 4.4.11, which contain fixes that prevent the race condition from occurring during symlink resolution. Additional protective measures include implementing strict file system permissions, monitoring for suspicious symlink creation patterns, and reviewing share definitions to ensure proper access controls are in place. Network segmentation and limiting direct client access to Samba servers can also reduce the attack surface. System administrators should also consider implementing intrusion detection systems that can monitor for unusual file access patterns that might indicate exploitation attempts. The vulnerability demonstrates the importance of proper synchronization in file system operations and highlights the need for thorough security testing of concurrent access scenarios in server applications, particularly those handling user file operations and access control decisions.