CVE-1999-0997 in wu-ftpd
Summary
by MITRE
wu-ftp with FTP conversion enabled allows an attacker to execute commands via a malformed file name that is interpreted as an argument to the program that does the conversion, e.g. tar or uncompress.
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Analysis
by VulDB Data Team • 01/12/2025
The vulnerability described in CVE-1999-0997 represents a critical command injection flaw within the wu-ftp server implementation when FTP conversion features are enabled. This vulnerability stems from improper input validation and sanitization of file names during the conversion process, creating a pathway for remote attackers to execute arbitrary commands on the affected system. The flaw specifically targets the interaction between the FTP server and conversion utilities such as tar and uncompress, which are commonly used for handling compressed files during file transfers.
The technical implementation of this vulnerability exploits the trust relationship between the FTP server and system utilities. When a user uploads or downloads a file with conversion enabled, the wu-ftp server passes the file name directly to the underlying conversion program without adequate sanitization. This creates a classic command injection scenario where attacker-controlled input can be interpreted as command-line arguments by programs like tar or uncompress. The vulnerability is particularly dangerous because it leverages legitimate system utilities that are typically trusted and available on most Unix-like systems, making detection more challenging.
From an operational perspective, this vulnerability allows attackers to achieve arbitrary code execution with the privileges of the ftp user account, which typically runs with limited system access but can potentially be escalated further. The impact extends beyond simple command execution to include potential privilege escalation, data exfiltration, and system compromise. Attackers can leverage this vulnerability to gain persistent access, install backdoors, or launch further attacks against the internal network. The vulnerability affects systems running wu-ftp versions that support conversion features, which were widely deployed in enterprise and academic environments during the late 1990s.
Security professionals should note this vulnerability aligns with CWE-78, which describes improper neutralization of special elements used in OS commands, and maps to ATT&CK technique T1059.007 for command and script injection. The flaw demonstrates the critical importance of input validation and the principle of least privilege in system design. Organizations should immediately implement mitigations including disabling FTP conversion features when not required, applying security patches to update wu-ftp implementations, and implementing network segmentation to limit exposure. Additional protective measures include monitoring FTP traffic for suspicious file name patterns, implementing host-based intrusion detection systems, and conducting regular security assessments of file transfer services. The vulnerability highlights the necessity of proper input sanitization and the dangers of executing system commands with user-provided data, making it a prime example of why secure coding practices are essential in network services.