CVE-2019-9949 in My Cloud Cloud
Summary
by MITRE
Western Digital My Cloud Cloud, Mirror Gen2, EX2 Ultra, EX2100, EX4100, DL2100, DL4100, PR2100 and PR4100 before firmware 2.31.183 are affected by a code execution (as root, starting from a low-privilege user session) vulnerability. The cgi-bin/webfile_mgr.cgi file allows arbitrary file write by abusing symlinks. Specifically, this occurs by uploading a tar archive that contains a symbolic link, then uploading another archive that writes a file to the link using the "cgi_untar" command. Other commands might also be susceptible. Code can be executed because the "name" parameter passed to the cgi_unzip command is not sanitized.
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Analysis
by VulDB Data Team • 06/15/2020
This vulnerability affects a range of Western Digital My Cloud storage devices including various models from the Mirror Gen2, EX2 Ultra, EX2100, EX4100, DL2100, DL4100, PR2100, and PR4100 series. The flaw exists in the webfile_mgr.cgi component that handles file operations through the cgi-bin directory. The vulnerability enables a low-privilege user to achieve root code execution through a sophisticated attack chain involving symbolic link manipulation and arbitrary file writing capabilities.
The technical implementation of this vulnerability stems from improper input validation within the cgi_unzip command where the "name" parameter is not adequately sanitized. This allows attackers to manipulate the extraction process by creating malicious tar archives containing symbolic links. The attack proceeds in two phases where the first archive establishes a symbolic link and the second archive writes malicious content to that link location. The cgi_untar command then executes with the attacker-controlled parameters, creating a path traversal condition that ultimately leads to arbitrary code execution with root privileges.
This vulnerability represents a critical security flaw that directly violates multiple security principles including input validation, privilege separation, and secure file handling practices. The attack vector demonstrates a classic path traversal exploit combined with symbolic link manipulation, allowing privilege escalation from unauthenticated user access to full system compromise. The vulnerability affects firmware versions prior to 2.31.183, indicating that Western Digital had not yet patched this fundamental flaw in their web interface handling.
The operational impact of this vulnerability is severe as it provides attackers with complete system control over affected devices. Once exploited, attackers can modify system files, install backdoors, exfiltrate stored data, and potentially use the compromised device as a pivot point for attacking other systems on the network. The vulnerability affects not just individual device security but also poses risks to network infrastructure since these storage devices often serve as central points for data access and sharing. The attack requires minimal privileges initially, making it particularly dangerous as it can be exploited by anyone with access to the device's web interface.
Security mitigations for this vulnerability include immediate firmware updates to version 2.31.183 or later where Western Digital has addressed the input sanitization issues. Network segmentation and access controls should be implemented to limit exposure of these devices to untrusted networks. Additionally, monitoring for unusual file upload patterns and system behavior should be enabled to detect potential exploitation attempts. The vulnerability aligns with CWE-22 Path Traversal and CWE-77 Command Injection categories, and represents a technique that could be categorized under ATT&CK technique T1059 Command and Scripting Interpreter for code execution. Organizations should also implement network-based intrusion detection systems to monitor for known exploit signatures targeting these specific device models and firmware versions.