CVE-2019-9668 in FTP
Summary
by MITRE
An issue was discovered in rovinbhandari FTP through 2012-03-28. receive_file in file_transfer_functions.c allows remote attackers to cause a denial of service (daemon crash) via a 0xffff datalen field value.
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Analysis
by VulDB Data Team • 03/19/2024
The vulnerability identified as CVE-2019-9668 represents a critical denial of service flaw within the rovinbhandari FTP implementation, specifically affecting versions through 2012-03-28. This issue resides in the file_transfer_functions.c module where the receive_file function processes incoming file transfer requests. The vulnerability stems from inadequate input validation mechanisms that fail to properly handle malformed datalen field values, creating an exploitable condition that can be leveraged by remote attackers to disrupt service availability. The affected FTP implementation demonstrates a classic buffer over-read or integer overflow scenario where the system attempts to process an excessively large datalen value of 0xffff, which exceeds normal file transfer parameters and causes the daemon to crash.
The technical exploitation of this vulnerability occurs when a remote attacker sends a specially crafted FTP command containing a 0xffff datalen field value to the vulnerable FTP daemon. This specific value represents the maximum possible unsigned short integer, which when processed by the receive_file function triggers an improper handling of the data length parameter. The function fails to validate that the datalen field falls within acceptable bounds for a legitimate file transfer operation, leading to a memory access violation or arithmetic overflow that ultimately results in the daemon process termination. This type of vulnerability aligns with CWE-129, which addresses improper validation of array indices, and CWE-191, which covers integer underflow or overflow conditions. The flaw demonstrates poor defensive programming practices where input validation is insufficient to prevent malicious or malformed data from causing system instability.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be exploited by attackers to create persistent availability issues for FTP services. When an FTP daemon crashes due to this vulnerability, legitimate users lose access to file transfer capabilities, potentially disrupting business operations that depend on FTP connectivity for data exchange. The remote nature of the attack means that adversaries can exploit this vulnerability from any location without requiring physical access to the system, making it particularly dangerous in networked environments. Organizations relying on this outdated FTP implementation face increased risk of service degradation and potential data loss incidents, especially in scenarios where FTP services are critical for business operations or integration with other systems.
Mitigation strategies for this vulnerability should prioritize immediate remediation through software updates or patches provided by the vendor, though given the age of the affected implementation, such updates may not be available. Organizations should implement network-level controls such as firewall rules that restrict FTP access to trusted networks and monitor for suspicious datalen field values in FTP traffic. Additionally, deploying intrusion detection systems that can identify and alert on anomalous FTP protocol behavior can help detect exploitation attempts. System administrators should consider implementing redundant FTP services or alternative file transfer protocols such as SFTP or FTPS to reduce dependency on the vulnerable implementation. The vulnerability also highlights the importance of maintaining up-to-date security practices and regularly reviewing legacy software components for known security flaws, as referenced in the MITRE ATT&CK framework's methodology for identifying and addressing system vulnerabilities through proper input validation and access control measures.