CVE-1999-0671 in NextFTP
Summary
by MITRE
Buffer overflow in ToxSoft NextFTP client through CWD command.
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Analysis
by VulDB Data Team • 03/14/2025
The vulnerability identified as CVE-1999-0671 represents a critical buffer overflow flaw within the ToxSoft NextFTP client software that specifically manifests during the processing of the CWD (Change Working Directory) command. This issue stems from inadequate input validation mechanisms within the client application's command handling routine, where user-supplied data is directly copied into fixed-length buffers without proper bounds checking. The vulnerability was discovered in a widely used ftp client software that was prevalent during the late 1990s era of internet connectivity and file transfer operations.
The technical implementation of this buffer overflow occurs when the NextFTP client receives a CWD command containing excessively long directory path specifications that exceed the allocated buffer space. This condition allows an attacker to overwrite adjacent memory locations within the application's process space, potentially leading to arbitrary code execution or application crash. The flaw resides in the client's handling of user input through the command line interface or automated scripts, where the software fails to validate the length of directory names before copying them into internal storage buffers. This type of vulnerability is classified under CWE-121 as a stack-based buffer overflow, where the buffer is located on the stack and overflow leads to overwriting adjacent stack variables and potentially the return address of the calling function.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it provides potential attackers with pathways for remote code execution within the context of the user running the NextFTP client. When exploited, the buffer overflow could allow malicious actors to inject and execute arbitrary code on the victim's system, potentially leading to complete system compromise. The vulnerability is particularly dangerous because ftp clients often run with elevated privileges and may be used to transfer sensitive data, making the exploitation of such flaws a significant concern for enterprise environments. The attack vector is typically executed through specially crafted ftp server responses or malicious ftp servers that send oversized CWD command responses to the vulnerable client software.
Mitigation strategies for this vulnerability involve immediate software updates and patches provided by the vendor, as well as network-level restrictions such as firewall rules that prevent access to potentially malicious ftp servers. System administrators should also implement input validation measures on ftp client configurations and consider disabling unnecessary ftp client features that could be exploited. Additionally, security monitoring should be enhanced to detect unusual ftp client behavior or attempts to send oversized command parameters. This vulnerability aligns with ATT&CK technique T1210 which describes exploitation of weaknesses in remote services, and represents a classic example of how legacy software vulnerabilities continue to pose risks even decades after their initial discovery. Organizations should prioritize patch management processes to address such historical vulnerabilities that may still exist in deployed systems, particularly in environments where older ftp client software remains in use.