CVE-2019-9648 in FTP Server
Summary
by MITRE
An issue was discovered in the SFTP Server component in Core FTP 2.0 Build 674. A directory traversal vulnerability exists using the SIZE command along with a \..\..\ substring, allowing an attacker to enumerate file existence based on the returned information.
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Analysis
by VulDB Data Team • 06/13/2024
The vulnerability identified as CVE-2019-9648 represents a critical directory traversal flaw within the SFTP Server component of Core FTP version 2.0 Build 674. This security weakness stems from inadequate input validation and path sanitization mechanisms that fail to properly handle maliciously crafted file path references. The vulnerability specifically manifests when processing the SIZE command with directory traversal sequences such as \..\..\ which allows unauthorized access to files outside the intended directory structure. This issue falls under the Common Weakness Enumeration category CWE-22, which catalogs improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal attacks.
The technical exploitation of this vulnerability occurs through the manipulation of SFTP commands where an attacker can construct malicious file paths that bypass normal access controls. When the SIZE command processes a path containing the \..\.. sequence, the server fails to adequately validate the input, allowing the traversal to occur and potentially exposing sensitive files or directories that should remain inaccessible. The system's response to such requests reveals information about file existence, enabling attackers to enumerate files and potentially identify valuable targets for further exploitation. This enumeration capability provides attackers with detailed knowledge of the server's file structure and can facilitate more sophisticated attacks including data exfiltration or system compromise.
The operational impact of CVE-2019-9648 extends beyond simple information disclosure, as it creates a foundation for more serious security breaches. Attackers can leverage this vulnerability to map the entire file system structure, identify sensitive configuration files, user data, or system binaries, and subsequently target these resources for exploitation. The vulnerability is particularly dangerous in environments where Core FTP serves as a primary file transfer mechanism, as it can provide attackers with unauthorized access to critical organizational data. This type of vulnerability aligns with ATT&CK technique T1083, which covers discovering file and directory permissions, and T1005, which involves data from local system, making it a valuable reconnaissance tool for threat actors seeking to understand system configurations and data layouts.
Organizations utilizing Core FTP should implement immediate mitigations including updating to the latest version that addresses this vulnerability, implementing proper input validation for all SFTP commands, and establishing network-level restrictions that limit access to the SFTP server. Additional protective measures include configuring the server to operate in a restricted environment with minimal file system access, implementing strict access controls, and monitoring for suspicious SFTP activity patterns. The vulnerability demonstrates the importance of proper input sanitization and access control enforcement in network services, particularly those handling file system operations. Security teams should also consider implementing intrusion detection systems that can identify and alert on suspicious path traversal attempts, as well as conducting regular vulnerability assessments to identify similar weaknesses in other network services and applications.