Any server running a version prior to and including ProFTPD (1.2.0pre1), wu-ftp 2.6.0(1), OpenBSD 6.4, beroFTP (prior to 10 June 2000), HP FTP 1.7.214.5, or IAX Version 4.3 are vulnerable to exploit. In addition, versions (not patched or upgraded prior to 15 March 2001) of FTP from Sun, Silicon Graphics, HP, and others may also be vulnerable to exploit.
In addition, certain FTP servers (e.g., War FTP) allow directory traversal outside of the anonymous root directory.
There is a general class of vulnerability that exists in several popular ftp servers. Due to insufficient bounds checking, it is possible to subvert an ftp server by corrupting its internal stack space. By supplying carefully designed commands to the ftp server, intruders can force the server to execute arbitrary commands with root privilege. On most vulnerable systems, the ftpd software is installed and enabled by default.
Currently there are several ways to exploit the ftp servers in question. One temporary workaround against an anonymous attack is to disable any world writable directories the user may have access to by making them read only. This will prevent an attacker from building an unusually large path, which is required in order to execute many of attacks. Directory traversal problems can be eliminated by patching to the current version. Wherever possible, anonymous ftp access should be disabled! The permanent solution is to install a patch from your Vendor, or locate one provided by the Software's author or maintainer.
You may read more about this vulnerability in CERT Advisory 99.03, CERT Advisory 2000-13, and www.securityfocus.com/advisories/3680