RHEL 6 Security Guide - 2.2.6. Securing FTP

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2.2.6. Securing FTP

The File Transfer Protocol (FTP) is an older TCP protocol designed to transfer files over a network. Because all transactions with the server, including user authentication, are unencrypted, it is considered an insecure protocol and should be carefully configured.

Red Hat Enterprise Linux provides three FTP servers.

gssftpd — A Kerberos-aware xinetd-based FTP daemon that does not transmit authentication information over the network.
Red Hat Content Accelerator (tux) — A kernel-space Web server with FTP capabilities.
vsftpd — A standalone, security oriented implementation of the FTP service.

The following security guidelines are for setting up the vsftpd FTP service.

2.2.6.1. FTP Greeting Banner

Before submitting a username and password, all users are presented with a greeting banner. By default, this banner includes version information useful to crackers trying to identify weaknesses in a system.

To change the greeting banner for vsftpd, add the following directive to the /etc/vsftpd/vsftpd.conf file:

ftpd_banner=<insert_greeting_here>

Replace <insert_greeting_here> in the above directive with the text of the greeting message.

For mutli-line banners, it is best to use a banner file. To simplify management of multiple banners, place all banners in a new directory called /etc/banners/. The banner file for FTP connections in this example is /etc/banners/ftp.msg. Below is an example of what such a file may look like:

######### # Hello, all activity on ftp.example.com is logged. #########

Note

It is not necessary to begin each line of the file with 220 as specified in Section 2.2.1.1.1, “TCP Wrappers and Connection Banners”.

To reference this greeting banner file for vsftpd, add the following directive to the /etc/vsftpd/vsftpd.conf file:

banner_file=/etc/banners/ftp.msg

It also is possible to send additional banners to incoming connections using TCP Wrappers as described in Section 2.2.1.1.1, “TCP Wrappers and Connection Banners”.