CVE-1999-1333 in ncftp
Summary
by MITRE
automatic download option in ncftp 2.4.2 FTP client in Red Hat Linux 5.0 and earlier allows remote attackers to execute arbitrary commands via shell metacharacters in the names of files that are to be downloaded.
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Analysis
by VulDB Data Team • 04/20/2026
The vulnerability described in CVE-1999-1333 represents a critical command injection flaw within the ncftp 2.4.2 FTP client implementation in Red Hat Linux 5.0 and earlier versions. This issue stems from the automatic download functionality that processes file names without proper sanitization of special shell metacharacters. The vulnerability falls under the category of CWE-78 Improper Neutralization of Special Elements used in an OS Command, which is a fundamental weakness in input validation and command construction. Attackers can exploit this by crafting malicious file names containing shell metacharacters such as semicolons, ampersands, or backticks that get executed when the client processes automatic downloads. The flaw exists specifically in the client-side processing logic where file names are directly incorporated into shell commands without proper escaping or filtering mechanisms.
The operational impact of this vulnerability extends beyond simple command execution to potentially allow full system compromise when attackers leverage the automatic download feature. An attacker who can influence file names in an FTP session can execute arbitrary commands with the privileges of the user running the ncftp client. This creates a significant risk in environments where users might download files from untrusted FTP servers or where automated download processes are configured to run without proper user intervention. The vulnerability is particularly dangerous because it operates at the client level and can be triggered automatically without user interaction, making it a stealthy attack vector. According to ATT&CK framework, this maps to T1059.004 Command and Scripting Interpreter: Unix Shell, where adversaries use shell commands to execute malicious payloads.
Mitigation strategies for CVE-1999-1333 require immediate patching of the ncftp client to version 2.4.3 or later, which includes proper input sanitization for file names. System administrators should also implement network segmentation to limit FTP access to trusted networks and disable automatic download features where possible. Additional protective measures include configuring the FTP client to sanitize all file names before processing, implementing proper input validation that filters or escapes shell metacharacters, and monitoring for unusual command execution patterns. The vulnerability highlights the importance of proper input validation in client-side applications and demonstrates how seemingly innocuous features like automatic downloads can become attack vectors when proper security controls are not implemented. Organizations should also consider implementing network-based intrusion detection systems to monitor for suspicious FTP traffic patterns and shell command execution that could indicate exploitation attempts.