CVE-2004-1992 in Serv-U FTP Server
Summary
by MITRE
Buffer overflow in Serv-U FTP server before 5.0.0.6 allows remote attackers to cause a denial of service (crash) via a long -l parameter, which triggers an out-of-bounds read.
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Analysis
by VulDB Data Team • 08/06/2025
The vulnerability identified as CVE-2004-1992 represents a critical buffer overflow flaw within the Serv-U FTP server software, specifically affecting versions prior to 5.0.0.6. This issue resides in the server's handling of command-line parameters, particularly the -l parameter which is used for logging or list operations. The flaw occurs when the server receives an excessively long -l parameter that exceeds the allocated buffer space, leading to memory corruption that can be exploited by remote attackers to crash the service.
The technical implementation of this vulnerability stems from improper input validation and buffer management within the Serv-U FTP server's command processing logic. When a remote attacker submits a malformed -l parameter containing more data than the server's internal buffer can accommodate, the program attempts to write beyond the allocated memory boundaries. This out-of-bounds read condition results in undefined behavior that manifests as a service crash or complete system termination. The vulnerability operates at the application layer and requires no authentication, making it particularly dangerous as it can be exploited by anyone with network access to the affected FTP server.
From an operational impact perspective, this vulnerability creates significant risk for organizations relying on Serv-U FTP servers for file transfer operations. The denial of service condition effectively renders the FTP service unavailable to legitimate users, potentially disrupting business operations and data exchange processes. The attack vector is straightforward and can be executed remotely, requiring minimal technical expertise from attackers. Organizations may experience service interruptions, loss of productivity, and potential data accessibility issues that could affect customer relationships and operational continuity. The vulnerability also creates opportunities for more sophisticated attacks if attackers can leverage the crash to execute additional malicious code or establish persistent access points.
The vulnerability maps to CWE-121, which describes heap-based buffer overflow conditions, and aligns with ATT&CK technique T1499.004 for network denial of service attacks. Organizations should implement immediate mitigations including applying the vendor-provided patch to upgrade to Serv-U version 5.0.0.6 or later, which addresses the buffer overflow through proper input length validation and memory boundary checks. Network-level protections such as firewall rules restricting FTP access to trusted IP addresses and implementing rate limiting can provide additional defense-in-depth measures. Regular vulnerability assessments and security monitoring should be conducted to identify similar issues in other FTP server implementations and ensure comprehensive protection against similar buffer overflow vulnerabilities that could compromise system availability and integrity.