CVE-2009-4051 in Home FTP Server
Summary
by MITRE
Home FTP Server 1.10.1.139 allows remote attackers to cause a denial of service (daemon outage) via multiple invalid SITE INDEX commands.
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Analysis
by VulDB Data Team • 09/29/2025
The vulnerability identified as CVE-2009-4051 affects Home FTP Server version 1.10.1.139, representing a critical denial of service flaw that can be exploited by remote attackers to disrupt service availability. This vulnerability specifically manifests through the processing of multiple invalid SITE INDEX commands, which are part of the FTP protocol's extended command set used for server-specific operations. The issue stems from inadequate input validation and error handling within the server's command processing logic, where the daemon fails to properly sanitize or reject malformed SITE INDEX commands that exceed expected parameters or format requirements.
The technical flaw resides in the server's inability to gracefully handle malformed or excessive SITE INDEX commands, leading to daemon instability and eventual service outage. When multiple invalid SITE INDEX commands are sent in sequence or with malformed parameters, the Home FTP Server process becomes overwhelmed by the malformed inputs and subsequently crashes or becomes unresponsive. This behavior aligns with CWE-129, which describes improper validation of input boundaries, and CWE-20, which covers inputs that are not properly validated. The vulnerability operates at the application layer of the network stack and can be exploited without authentication requirements, making it particularly dangerous in environments where FTP services are exposed to untrusted networks.
The operational impact of this vulnerability extends beyond simple service disruption, as it can lead to complete loss of file transfer capabilities for legitimate users and may require manual intervention to restore service. Organizations relying on Home FTP Server for file sharing operations face potential business disruption, especially in scenarios where the service is critical for operations or where automated processes depend on FTP connectivity. The vulnerability also represents a potential vector for more sophisticated attacks, as the service outage could be used as a distraction while attackers perform other malicious activities. According to ATT&CK framework, this vulnerability maps to T1499.004, which covers network denial of service attacks, and T1566.002, which involves spearphishing with malicious attachments, as attackers could potentially use this vulnerability as part of broader attack campaigns.
Mitigation strategies for CVE-2009-4051 should focus on immediate patching of the Home FTP Server software to the latest available version that addresses the input validation issues. Network-level protections including firewall rules that limit FTP command processing and rate limiting of SITE commands can provide temporary protection while patches are deployed. Additionally, implementing monitoring solutions that detect unusual command patterns or excessive SITE INDEX requests can help identify exploitation attempts before they cause service disruption. System administrators should also consider implementing intrusion detection systems that can identify the specific malformed command patterns associated with this vulnerability. The long-term solution involves adopting more robust FTP server implementations that follow secure coding practices and proper input validation mechanisms, as outlined in industry standards such as the OWASP Secure Coding Practices and ISO/IEC 27001 security requirements for information security management.