CVE-2019-9649 in FTP
Summary
by MITRE
An issue was discovered in the SFTP Server component in Core FTP 2.0 Build 674. Using the MDTM FTP command, a remote attacker can use a directory traversal technique (..\..\) to browse outside the root directory to determine the existence of a file on the operating system, and its last modified date.
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Analysis
by VulDB Data Team • 06/13/2024
The vulnerability identified as CVE-2019-9649 represents a critical directory traversal flaw within the SFTP Server component of Core FTP version 2.0 Build 674. This issue stems from inadequate input validation and path handling mechanisms that fail to properly sanitize user-supplied paths during file system operations. The vulnerability specifically manifests through the MDTM FTP command which is designed to retrieve file modification timestamps, but can be exploited to perform unauthorized directory traversal attacks.
The technical implementation of this vulnerability allows remote attackers to manipulate file paths by injecting directory traversal sequences such as ..\..\. When the SFTP server processes these malformed paths through the MDTM command, it fails to properly validate the input against the configured root directory boundaries. This validation failure enables attackers to navigate outside the intended file system scope and access files that should remain restricted. The exploitation technique leverages the server's inability to properly resolve relative paths and maintain proper directory isolation, effectively bypassing access controls that should protect the underlying operating system.
The operational impact of CVE-2019-9649 extends beyond simple information disclosure, as it provides attackers with detailed knowledge of the target system's file structure and modification timestamps. This reconnaissance capability can serve as a foundation for more sophisticated attacks, enabling threat actors to map the file system hierarchy and identify potentially sensitive files or directories. The vulnerability can be exploited without authentication, making it particularly dangerous as it allows for passive reconnaissance that can be performed by anyone with network access to the affected server. From a cybersecurity perspective, this vulnerability directly violates the principle of least privilege and can enable further exploitation attempts.
Security professionals should note that this vulnerability aligns with CWE-22 (Improper Limitation of a Pathname to a Restricted Directory) and represents a classic example of path traversal attacks that have been documented across numerous applications and systems. The attack pattern follows established techniques described in the MITRE ATT&CK framework under the T1083 (File and Directory Discovery) technique, where adversaries gather information about the file system structure to plan further malicious activities. Organizations should implement immediate mitigations including input validation, path normalization, and proper access control enforcement. The recommended remediation involves updating to a patched version of Core FTP, implementing proper path validation mechanisms, and configuring the SFTP server to reject any path traversal attempts through the MDTM command. Additionally, network segmentation and monitoring should be enhanced to detect unusual file system access patterns that may indicate exploitation attempts.