CVE-2009-3655 in Serv-U
Summary
by MITRE
Rhino Software Serv-U 7.0.0.1 through 8.2.0.3 allows remote attackers to cause a denial of service (server crash) via unspecified vectors related to the "SITE SET TRANSFERPROGRESS ON" FTP command.
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Analysis
by VulDB Data Team • 03/25/2025
The vulnerability identified as CVE-2009-3655 affects Rhino Software Serv-U FTP server versions ranging from 7.0.0.1 through 8.2.0.3, representing a significant denial of service weakness that can be exploited remotely by attackers. This vulnerability specifically targets the server's handling of the "SITE SET TRANSFERPROGRESS ON" FTP command, which is used to enable transfer progress reporting during file transfers. The flaw manifests as a server crash that completely disrupts service availability for legitimate users and can be triggered without authentication, making it particularly dangerous in production environments where continuous service availability is critical.
The technical nature of this vulnerability stems from improper input validation and memory handling within the Serv-U FTP server implementation. When the maliciously crafted "SITE SET TRANSFERPROGRESS ON" command is processed, the server fails to properly validate or sanitize the command parameters, leading to a condition where memory corruption or stack overflow occurs. This type of vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and CWE-125, which covers out-of-bounds read errors. The vulnerability represents a classic example of how improper handling of user-supplied data can lead to catastrophic system failures, particularly in network services that must process untrusted input from remote clients.
From an operational impact perspective, this vulnerability creates substantial risk for organizations relying on Serv-U FTP servers for file transfer operations. The remote exploitation capability means that attackers can cause service disruption from anywhere on the network without requiring local access or authentication credentials, making it an attractive target for malicious actors seeking to disrupt business operations. The server crash resulting from this vulnerability effectively renders the FTP service unavailable until manual intervention or system restart occurs, potentially causing significant downtime for critical file transfer processes. This denial of service condition can be particularly damaging in environments where automated file transfers, backup operations, or customer-facing file sharing services depend on the FTP server's availability.
The exploitation of this vulnerability can be categorized under ATT&CK technique T1499.004, which describes network denial of service attacks targeting remote services. Organizations should implement immediate mitigation strategies including applying the vendor-supplied patches and updates that address the specific memory handling flaws in the affected Serv-U versions. Network segmentation and firewall rules can help limit exposure by restricting access to the FTP service to trusted networks only, while monitoring systems should be configured to detect unusual patterns of FTP command usage that might indicate exploitation attempts. Additionally, implementing redundant FTP services or alternative file transfer protocols can provide resilience against this specific class of denial of service attacks, ensuring business continuity even when individual FTP servers are compromised. The vulnerability serves as a reminder of the importance of regular security updates and proper input validation in network services to prevent exploitation of memory corruption vulnerabilities.