CVE-2017-11156 in Download Station
Summary
by MITRE
Synology Download Station 3.8.x before 3.8.5-3475 and 3.x before 3.5-2984 uses weak permissions (0777) for ui/dlm/btsearch directory, which allows remote authenticated users to execute arbitrary code by uploading an executable via unspecified vectors.
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Analysis
by VulDB Data Team • 12/15/2022
The vulnerability identified as CVE-2017-11156 affects Synology Download Station versions prior to specific patches, creating a critical security risk through improper file system permissions. This flaw exists in both the 3.8.x series before 3.8.5-3475 and the 3.x series before 3.5-2984, representing a significant oversight in the application's security architecture that could enable remote code execution attacks.
The core technical flaw involves the use of weak permissions set to 0777 for the ui/dlm/btsearch directory within the Download Station application. This permission setting grants full read, write, and execute access to all users, including authenticated remote users who should not possess such extensive privileges. The 0777 permission structure violates fundamental security principles by eliminating access controls that should restrict file operations to authorized system components. This misconfiguration creates an exploitable path where malicious actors can upload executable files directly to the vulnerable directory, bypassing normal security boundaries that would typically prevent such operations.
The operational impact of this vulnerability is severe and directly enables remote code execution capabilities for authenticated users. Attackers who can authenticate to the Download Station service can leverage this weakness to upload malicious executables to the btsearch directory, which then becomes executable within the application context. This creates a persistent threat vector that could allow attackers to establish backdoors, escalate privileges, or deploy additional malware within the affected system. The unspecified vectors mentioned in the description suggest that the attack surface may be broader than initially apparent, potentially encompassing multiple upload mechanisms or file handling processes within the application's architecture.
This vulnerability aligns with CWE-732, which describes improper permission assignment, and represents a classic example of inadequate access control implementation. The flaw also maps to ATT&CK technique T1059, specifically command and script injection, as attackers can execute arbitrary code through uploaded files. The weakness demonstrates poor least privilege implementation and highlights the importance of proper directory permissions in web applications. Organizations using affected versions of Synology Download Station face significant risk of compromise, particularly in environments where the application is exposed to untrusted users or where authentication mechanisms might be bypassed.
Mitigation strategies should include immediate patching to the affected versions, specifically upgrading to Download Station 3.8.5-3475 or later for the 3.8.x series, and 3.5-2984 or later for the 3.x series. System administrators should also manually verify and correct the permissions on the ui/dlm/btsearch directory, ensuring that appropriate access controls are enforced and that the directory does not maintain world-writable permissions. Additional defensive measures include implementing network segmentation, monitoring for unauthorized file uploads, and conducting regular security assessments of web applications to identify similar permission-related vulnerabilities. The incident underscores the critical importance of maintaining proper file system permissions and access controls as fundamental security practices in application development and deployment.