Enhancing Security With Xinetd - Red Hat ENTERPRISE LINUX 5 - DEPLOYMENT Deployment Manual

The %c token supplies a variety of client information, such as the username and hostname, or the
username and IP address to make the connection even more intimidating.
For this banner to be displayed to incoming connections, add the following line to the /etc/
hosts.allow file:
vsftpd : ALL : banners /etc/banners/
43.2.1.1.2. TCP Wrappers and Attack Warnings
If a particular host or network has been detected attacking the server, TCP Wrappers can be used to
warn the administrator of subsequent attacks from that host or network using the spawn directive.
In this example, assume that a cracker from the 206.182.68.0/24 network has been detected
attempting to attack the server. Place the following line in the /etc/hosts.deny file to deny any
connection attempts from that network, and to log the attempts to a special file:
ALL : 206.182.68.0 : spawn /bin/ 'date' %c %d >> /var/log/intruder_alert
The %d token supplies the name of the service that the attacker was trying to access.
To allow the connection and log it, place the spawn directive in the /etc/hosts.allow file.
Note
Because the spawn directive executes any shell command, create a special script to
notify the administrator or execute a chain of commands in the event that a particular
client attempts to connect to the server.
43.2.1.1.3. TCP Wrappers and Enhanced Logging
If certain types of connections are of more concern than others, the log level can be elevated for that
service using the severity option.
For this example, assume that anyone attempting to connect to port 23 (the Telnet port) on an FTP
server is a cracker. To denote this, place an emerg flag in the log files instead of the default flag,
info, and deny the connection.
To do this, place the following line in /etc/hosts.deny:
in.telnetd : ALL : severity emerg
This uses the default authpriv logging facility, but elevates the priority from the default value of
info to emerg, which posts log messages directly to the console.

43.2.1.2. Enhancing Security With xinetd

This section focuses on using xinetd to set a trap service and using it to control resource levels
available to any given xinetd service. Setting resource limits for services can help thwart Denial of
Securing Services With TCP Wrappers and xinetd
623