Source: cve@mitre.org
Multiple directory traversal vulnerabilities in the FileBrowser components in Synology DiskStation Manager (DSM) before 4.3-3810 Update 3 allow remote attackers to read, write, and delete arbitrary files via a .. (dot dot) in the (1) path parameter to file_delete.cgi or (2) folder_path parameter to file_share.cgi in webapi/FileStation/; (3) dlink parameter to fbdownload/; or unspecified parameters to (4) html5_upload.cgi, (5) file_download.cgi, (6) file_sharing.cgi, (7) file_MVCP.cgi, or (8) file_rename.cgi in webapi/FileStation/.
Synology DiskStation Manager (DSM) versions prior to 4.3-3810 Update 3 are vulnerable to multiple directory traversal flaws. These vulnerabilities allow remote attackers to gain unauthorized access to the file system, enabling them to read, write, and delete arbitrary files, potentially leading to complete system compromise.
Step 1: Target Identification: Identify a vulnerable Synology DiskStation Manager (DSM) instance running a version prior to 4.3-3810 Update 3.
Step 2: Parameter Injection: Craft a malicious request targeting one of the vulnerable CGI scripts (e.g., file_delete.cgi, file_share.cgi) and include a .. sequence in the relevant parameter (e.g., path, folder_path, dlink).
Step 3: Path Traversal: The .. sequence is interpreted by the server, allowing the attacker to navigate up the directory tree.
Step 4: File Access/Manipulation: By strategically placing .. sequences, the attacker can access, read, write, or delete arbitrary files on the system, depending on the script and the intended action (e.g., deleting a configuration file, uploading a malicious web shell, or accessing sensitive data).
Step 5: Exploitation: The attacker leverages the ability to manipulate files to achieve their objectives, which could include gaining remote code execution, data exfiltration, or denial of service.
The root cause of CVE-2013-6987 lies in insufficient input validation and sanitization within the FileBrowser components of Synology DSM. Specifically, the affected CGI scripts (file_delete.cgi, file_share.cgi, fbdownload/, html5_upload.cgi, file_download.cgi, file_sharing.cgi, file_MVCP.cgi, and file_rename.cgi) fail to properly validate user-supplied input, particularly the path or folder_path parameters. This lack of validation allows attackers to inject .. (dot-dot) sequences into these parameters, effectively traversing the directory structure and accessing files outside of the intended scope. The vulnerability is a classic example of a path traversal attack, exploiting the system's failure to prevent access to restricted directories. The scripts do not adequately check the provided file paths, leading to the potential for arbitrary file access, modification, and deletion. The flaw is not a buffer overflow or race condition, but a logic error in input handling.
While no specific APT groups are definitively linked to this specific CVE, the ease of exploitation and the potential for complete system compromise make it attractive to various threat actors. The vulnerability could be used as an initial access vector for ransomware attacks or data theft. This vulnerability is not listed in the CISA KEV at the time of this report, but it is a high-severity vulnerability that should be addressed immediately.
Monitor web server logs (e.g., Apache access logs) for suspicious requests containing .. sequences in the URL path, especially targeting the identified CGI scripts (file_delete.cgi, file_share.cgi, fbdownload/, html5_upload.cgi, file_download.cgi, file_sharing.cgi, file_MVCP.cgi, and file_rename.cgi).
Analyze network traffic for unusual HTTP requests with long or complex URL paths, particularly those involving file operations.
Implement file integrity monitoring to detect unauthorized modifications to critical system files.
Use intrusion detection/prevention systems (IDS/IPS) with signatures specifically designed to detect directory traversal attempts.
Review system logs for evidence of unauthorized file access or modification attempts.
Update to the latest version of Synology DSM (4.3-3810 Update 3 or later). This is the primary and most effective remediation step.
Implement a Web Application Firewall (WAF) to filter malicious requests containing directory traversal attempts.
Configure strict file access permissions to limit the impact of a successful exploit. Ensure that the web server user has minimal privileges.
Regularly scan the system for vulnerabilities and apply security patches promptly.
Implement input validation and sanitization in custom web applications or scripts to prevent similar vulnerabilities.
Monitor system logs and network traffic for suspicious activity.