CVE-2001-1021 in WS FTP Server
Summary
by MITRE
Buffer overflows in WS_FTP 2.02 allow remote attackers to execute arbitrary code via long arguments to (1) DELE, (2) MDTM, (3) MLST, (4) MKD, (5) RMD, (6) RNFR, (7) RNTO, (8) SIZE, (9) STAT, (10) XMKD, or (11) XRMD.
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Analysis
by VulDB Data Team • 09/30/2025
The vulnerability identified as CVE-2001-1021 represents a critical buffer overflow flaw in WS_FTP 2.02, a widely used file transfer protocol client software. This vulnerability exists within the handling of specific FTP commands that process user-supplied arguments, creating a pathway for remote attackers to execute arbitrary code on affected systems. The flaw manifests when the software fails to properly validate the length of arguments passed to eleven distinct FTP commands including DELE, MDTM, MLST, MKD, RMD, RNFR, RNTO, SIZE, STAT, XMKD, and XRMD. The buffer overflow occurs because the application allocates fixed-size buffers to store command arguments without adequate bounds checking, allowing maliciously crafted input to overwrite adjacent memory locations.
The technical implementation of this vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions where insufficient bounds checking permits attackers to overwrite adjacent memory. This particular flaw operates at the application layer within the FTP client software, specifically targeting the argument parsing mechanisms of the mentioned commands. When an attacker sends a specially crafted command with an excessively long argument string, the buffer overflow can overwrite the return address on the stack or other critical program variables. This memory corruption enables attackers to redirect program execution flow and inject malicious code that executes with the privileges of the affected process, typically running with the permissions of the user account running WS_FTP.
The operational impact of CVE-2001-1021 extends beyond simple remote code execution, as it can lead to complete system compromise when the affected FTP client is running with elevated privileges. Attackers exploiting this vulnerability can gain unauthorized access to sensitive data, establish persistent backdoors, or use the compromised system as a launch point for further attacks within the network infrastructure. The vulnerability affects systems where WS_FTP 2.02 is installed and actively processing FTP commands, making it particularly dangerous in environments where FTP services are exposed to untrusted networks. The attack vector is particularly concerning because it requires no authentication for exploitation, allowing remote attackers to leverage the vulnerability from outside the network perimeter. This makes the vulnerability particularly attractive to threat actors who can exploit it without needing valid credentials, potentially enabling large-scale attacks against organizations with vulnerable FTP client installations.
The remediation approach for CVE-2001-1021 involves immediate software updates from the vendor to address the buffer overflow conditions in the WS_FTP client implementation. Organizations should prioritize patching affected systems and consider implementing network segmentation to limit exposure of FTP client installations to untrusted networks. Additionally, network monitoring should be enhanced to detect anomalous FTP command sequences that might indicate exploitation attempts. From an ATT&CK framework perspective, this vulnerability maps to techniques involving command and control communications and privilege escalation, as attackers can use the executed code to establish persistent access. System administrators should also consider implementing input validation measures at network boundaries and conducting regular vulnerability assessments to identify similar buffer overflow conditions in other legacy applications that may be running on the network infrastructure. The vulnerability demonstrates the critical importance of proper input validation and bounds checking in preventing exploitation of memory corruption flaws that have remained relevant in cybersecurity practices for over two decades.