CVE-2004-1135 in WS_FTP Server
Summary
by MITRE
Multiple buffer overflows in WS_FTP Server 5.03 2004.10.14 allow remote attackers to cause a denial of service (service crash) via long (1) SITE, (2) XMKD, (3) MKD, and (4) RNFR commands.
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Analysis
by VulDB Data Team • 07/06/2025
The vulnerability identified as CVE-2004-1135 represents a critical buffer overflow issue affecting WS_FTP Server version 5.03 build 2004.10.14, which was widely deployed in enterprise environments during the early 2000s for file transfer operations. This flaw specifically targets the server's handling of several key FTP commands including SITE, XMKD, MKD, and RNFR, making it particularly dangerous as these commands are fundamental to file system operations within FTP protocols. The vulnerability arises from insufficient input validation and boundary checking within the server's command processing routines, creating opportunities for malicious actors to exploit memory corruption patterns that can lead to complete service disruption.
The technical exploitation of this vulnerability occurs when remote attackers send specially crafted commands containing excessive data payloads to the affected FTP server. Each of the targeted commands - SITE, XMKD, MKD, and RNFR - processes user input without adequate bounds checking, allowing attackers to overflow the allocated buffer space and overwrite adjacent memory locations. This buffer overflow condition typically results in stack corruption or heap corruption depending on the specific implementation details, ultimately causing the WS_FTP Server process to terminate unexpectedly and crash the service. The vulnerability falls under CWE-121, which classifies buffer overflow conditions where insufficient bounds checking allows attackers to write past the end of allocated buffer space, and aligns with ATT&CK technique T1499.004 for network denial of service attacks targeting system services.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be leveraged for more sophisticated attacks within compromised networks. When an attacker successfully exploits this vulnerability, they can cause repeated service crashes that may lead to availability issues for legitimate users and potentially provide opportunities for additional exploitation attempts. The vulnerability affects organizations relying on WS_FTP Server for critical file transfer operations, particularly those in financial services, healthcare, and government sectors where uninterrupted access to file systems is essential. The exploitability of this vulnerability is relatively straightforward, requiring only basic FTP client capabilities to send malformed commands, making it a preferred target for both automated scanning tools and determined attackers seeking to disrupt services.
Organizations affected by this vulnerability should implement immediate mitigations including applying the vendor-supplied patches, implementing network segmentation to limit access to FTP services, and deploying intrusion detection systems to monitor for suspicious command sequences. The recommended remediation strategy involves upgrading to a patched version of WS_FTP Server or migrating to more modern FTP server implementations that properly handle input validation. Network administrators should also consider implementing access controls that restrict FTP command execution to trusted sources and monitor for unusual command patterns that might indicate exploitation attempts. Additionally, organizations should conduct comprehensive vulnerability assessments to identify other potentially affected systems and implement proper logging and monitoring to detect exploitation attempts. The vulnerability demonstrates the critical importance of proper input validation and memory management practices in server applications, serving as a reminder that even well-established FTP implementations can contain fundamental security flaws that can be exploited for denial of service attacks.