Kerberos4 ftp client is a simple ftp client, with the extensions defined by RFC 2228. When authentication fails with AUTH, client will use USER/PASS command as other ones. A bug in the code may cause a heap overflow which leads to remote code execution. The overflow occurs when the server responds to client's request for passive mode. If the server responds with a long reply in the place of IP and port, pasv buffer will overflow. Affected version: 4-1.1.1 The real danger: an ftp server can simply modified to recognize Kerberos4 ftp client by it's protocol. You know the rest. Details and exploit code: mantra.freeweb.hu Marcell Fodor