Security Warning Banners

File /etc/issue can be used to issue security warnings after login. It can contain, for example, the following text:

This system is a restricted access system. All activity on 
this system is subject to monitoring. If information collected
reveals possible criminal activity or activity that exceeds privileges,
evidence of such activity may be provided to the relevant authorities
for further action. By continuing past this point, you expressly consent
to this monitoring. 

Except on systems using CDE for login, this block of text will be displayed above the login prompt.

FTP Warning Banner

Returning a customized banner to FTP clients when they connect is a good idea, as it helps disguise what system the FTP server is running on. You can send banners to incoming connections either using TCP wrappers as described in the Section called TCP Wrappers and Connection Banners or as described below.

For vsftpd, add the following line to its xinetd configuration file, /etc/xinetd.d/vsftpd:

banner /etc/banners/warning.msg

For wu-ftpd add the exact same line to its configuration file, /etc/ftpaccess.

The contents of the banner file for vsftpd should look something like this:

220-Hello, all activity on ftp.example.com is logged.

Telnet banner

the telnet banner is in /etc/issue, but it does not work for the graphical login... 

SSH banner

The banner display from ssh is controlled in the /etc/ssh/sshd_config file. By default, ssh display the last login message on the tty when you login into the system by ssh.In the sshd_config file,there are three items are controlling the login messages.

They are:

PrintMotd yes/no -- SSH will display the contents in the /etc/motd,if you set this item to YES.

PrintLastLog yes/no -- This item to controlling if display the last login message ,such as login name, login time ...... Default value is true

Banner /path/to/file displaying the contents in the file which you are set by this item.

If you set both PrintMotd to true and Banner to a file /etc/motd you will get banner twice.

You can set the bannet to /etc/issue in Banner and set PrintMotd to no.

NEWS CONTENTS

• 190701 : Creating Login Banners ( Creating Login Banners, )

Old News ;-)

Creating Login Banners

UNIX Login Banners
===========================

The banners for UNIX machines depend on the particular vendor and service. For 
many recent systems (Sun, Linux), creating the file /etc/issue containing the 
banner text causes the banner text to be displayed before the console login 
and before all interactive logins such as telnet, rsh, and rlogin. 

For other systems and for services that do not respond to the /etc/issue file, 
put the banner text in the file /etc/motd. The contents of this file are 
displayed by the global /etc/.login and the /etc/profile files, depending on 
which shell you start (sh or csh), immediately after a successful login. 
Displaying the /etc/motd file immediately after login is also an option for 
the Secure Shell daemon (sshd) and is set in the /usr/local/etc/sshd_config 
file. 

Some versions of the FTP service have been modified to display, after login, 
the contents of the file .login_message found in the root directory of the FTP 
tree or in the users home directory. You will have to try this to see if it 
works. If it does not work, you must put a file named NOTICE_TO_USERS 
containing the warning text into the root directory of the anonymous ftp tree 
and the file or a link to the file into each user's home directory.

For machines that do not use these methods for displaying banners, consult the 
man pages for each service to see if there is a banner mechanism available.

NOTE: An important thing to note here is that if you remove a service from a 
UNIX machine, your machine will be more secure and you will not have to worry 
about placing a banner on that service. If you have open services that you do 
not need simply remove them.

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Last modified: March 12, 2019