The FTP server in AS/400 4.3, when running in IFS mode, allows remote attackers to obtain sensitive information via a symlink attack using RCMD and the ADDLNK utility, as demonstrated using the QSYS.LIB library.

The POP3 server in IBM iSeries AS/400 returns different error messages when the user exists or not, which allows remote attackers to determine valid user IDs on the server.

By design, the built-in FTP server for iSeries AS/400 systems does not support a restricted document root, which allows attackers to read or write arbitrary files, including sensitive QSYS databases, via a full pathname in a GET or PUT request.