CVE-2009-1668 in FTP Server
Summary
by MITRE
TYPSoft FTP Server 1.11 allows remote attackers to cause a denial of service (CPU consumption) by sending an ABOR (abort) command without an active file transfer.
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Analysis
by VulDB Data Team • 11/29/2024
The vulnerability identified as CVE-2009-1668 affects TYPSoft FTP Server version 1.11 and represents a denial of service flaw that can be exploited by remote attackers to consume excessive CPU resources. This issue arises from the server's improper handling of the ABOR command when no active file transfer is occurring. The ABOR command in FTP protocol is designed to abort an ongoing file transfer operation, but the vulnerable implementation fails to properly validate the command context before processing it. When an attacker sends an ABOR command without an active transfer, the server enters an infinite loop or excessive processing state that consumes significant CPU cycles, effectively rendering the service unavailable to legitimate users.
This vulnerability falls under the category of improper input validation and resource exhaustion, with direct implications for system availability and service integrity. The flaw demonstrates a classic lack of proper state management within the FTP server implementation, where the system fails to maintain accurate tracking of active transfer sessions. The issue is particularly concerning because it can be exploited remotely without authentication requirements, making it accessible to any attacker with network access to the server. The CPU consumption pattern suggests that the server's response to the malformed ABOR command triggers unnecessary processing loops or recursive function calls that continue until system resources are exhausted. According to CWE classification, this represents a CWE-400: Uncontrolled Resource Consumption vulnerability, which is a fundamental weakness in resource management that can lead to system instability and denial of service conditions.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be leveraged as part of larger attack campaigns targeting network availability. Attackers can repeatedly send ABOR commands to exhaust server resources, creating sustained denial of service conditions that may persist until the server is manually restarted or the system is rebooted. This makes the vulnerability particularly dangerous in environments where continuous availability is critical, such as enterprise file servers, web hosting platforms, or any infrastructure relying on FTP services for data transfer operations. The vulnerability also aligns with ATT&CK technique T1499.004, which involves network denial of service attacks through resource exhaustion, and demonstrates how basic protocol commands can be weaponized when server implementations lack proper error handling mechanisms.
Mitigation strategies for this vulnerability require immediate patching of the TYPSoft FTP Server to version 1.12 or later, which contains the necessary fixes for proper ABOR command handling. System administrators should implement network-level restrictions to limit FTP service access to trusted networks only, while also monitoring for unusual patterns of ABOR command usage that may indicate exploitation attempts. The fix should include proper state validation before processing ABOR commands, ensuring that the server only processes such commands when an actual transfer is in progress. Additional defensive measures include implementing rate limiting for FTP control commands, configuring intrusion detection systems to alert on suspicious ABOR command sequences, and establishing automated monitoring for CPU utilization spikes that could indicate exploitation. Organizations should also conduct comprehensive vulnerability assessments of their FTP infrastructure to identify similar implementation flaws in other server software, as this type of improper state management is common in legacy FTP implementations that were not designed with modern security considerations in mind.