CVE-2011-0203 in Mac OS X
Summary
by MITRE
Absolute path traversal vulnerability in xftpd in the FTP Server component in Apple Mac OS X before 10.6.8 allows remote attackers to list arbitrary directories by using the root directory as the starting point of a recursive listing.
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Analysis
by VulDB Data Team • 11/13/2021
The CVE-2011-0203 vulnerability represents a critical absolute path traversal flaw within the xftpd FTP server component of Apple Mac OS X systems prior to version 10.6.8. This vulnerability specifically affects the handling of recursive directory listing operations, where an attacker can exploit the lack of proper input validation to traverse the file system hierarchy from the root directory. The flaw exists in the way the FTP server processes directory listing commands, particularly when dealing with recursive operations that should be constrained to specific user-accessible directories but instead can be manipulated to access any location on the system. This issue falls under the CWE-22 category for Improper Limitation of a Pathname to a Restricted Directory, which is a fundamental security weakness in path traversal controls. The vulnerability demonstrates a classic example of insufficient input sanitization where user-supplied paths are not properly validated against the intended directory boundaries.
The technical implementation of this vulnerability stems from the FTP server's failure to properly restrict directory traversal operations within its recursive listing functionality. When a user requests a recursive directory listing, the xftpd service should limit the traversal to the user's designated home directory or assigned access scope. However, due to inadequate path validation mechanisms, attackers can manipulate the listing command to begin from the root directory and traverse the entire file system structure. This allows for arbitrary directory enumeration, potentially exposing sensitive system files, configuration data, and user information that should remain protected. The vulnerability is particularly dangerous because it enables attackers to gain comprehensive knowledge of the system's directory structure without requiring any authentication credentials for the initial traversal phase, making it a significant reconnaissance tool in broader attack campaigns.
The operational impact of this vulnerability extends beyond simple information disclosure to potentially enable more sophisticated attacks within the compromised system. Attackers can leverage this vulnerability to discover sensitive files such as configuration files, system logs, user credentials, and application data that may contain exploitable information. The ability to perform recursive directory listings from the root directory provides attackers with extensive mapping capabilities of the target system, which can be used to identify potential attack vectors, locate vulnerable services, or discover system-specific weaknesses. This vulnerability aligns with ATT&CK technique T1083 (File and Directory Discovery) and T1069 (Permission Groups Discovery), as it enables attackers to enumerate file systems and identify system access controls. The vulnerability also supports privilege escalation attempts by revealing system paths and file permissions that may not be accessible through normal user operations.
Mitigation strategies for CVE-2011-0203 should prioritize immediate system updates to Apple Mac OS X version 10.6.8 or later, which contain the necessary patches to address the path traversal vulnerability. System administrators should also implement network-level restrictions to limit FTP service access to trusted networks and consider disabling FTP services entirely in favor of more secure protocols such as SFTP or SCP. Additional defensive measures include implementing proper access controls and directory restrictions within the FTP server configuration, ensuring that users cannot traverse beyond their designated home directories, and monitoring FTP service logs for unusual directory listing activities. Organizations should also conduct regular security assessments to identify similar path traversal vulnerabilities in other services and applications, as this type of weakness often appears in systems that do not properly validate user inputs against system boundaries. The vulnerability demonstrates the critical importance of input validation and proper access control mechanisms in preventing unauthorized system enumeration and information disclosure attacks.