Getting Started with the Linux Intrusion Detection System

This article assumes that you have installed LIDS and its associated administration tools.

We will set up a system with tight security settings, and the services that will be allowed to run are MySQL, Apache and Bind.

The sample commands below assume that the Apache installation resides in /usr/local/apache, with a log directory of /var/log/httpd, and also assumes your Apache configuration directory is /etc/httpd. MySQL is assumed to be installed in /usr/local/mysql. Obviously, you'll want to change the commands to suit your installation if it differs.

It is beyond the scope of this article to cover everything necessary to secure your system completely. However, these examples of how access control is administered in LIDS should get you started.

After you restart LIDS, you can begin adding access controls to various system binaries and libraries. The following sets the /sbin, /bin, /usr/bin and /lib to read-only:

lidsconf -A -o /sbin -j READONLY

lidsconf -A -o /bin -j READONLY

lidsconf -A -o /usr/bin -j READONLY

lidsconf -A -o /lib -j READONLY

Next, we define some additional access controls for /opt, /etc and /usr/local/etc, which should be read-only, and we deny all access to /etc/shadow and the boot manager file:

lidsconf -A -o /etc -j READONLY

lidsconf -A -o /usr/local/etc -j READONLY

lidsconf -A -o /etc/shadow -j DENY

lidsconf -A -o /etc/lilo.conf -j DENY

Because we have denied all access to /etc/shadow, the system will not be able to authenticate logins, thus we need to allow login and vlock to have read-only access to the file. Additionally, su also should have read-only access to the /etc/shadow file:

lidsconf -A -s /bin/login -o /etc/shadow -j READONLY

lidsconf -A -s /usr/bin/vlock -o /etc/shadow -j READONLY

lidsconf -A -s /bin/su -o /etc/shadow -j READONLY

We need to set some other access controls for su, in order for it to work with UIDs and GIDs, and access the /etc/shadow file:

lidsconf -A -s /bin/su -o CAP_SETUID -j GRANT

lidsconf -A -s /bin/su -o CAP_SETGID -j GRANT

lidsconf -A -s /bin/su -o /etc/shadow -j READONLY

Now, we need to allow init, login and associated applications to have write access to log files:

lidsconf -A -o /var/log -j APPEND

lidsconf -A -s /bin/login -o /var/log/wtmp -j WRITE

lidsconf -A -s /bin/login -o /var/log/lastlog -j WRITE

lidsconf -A -s /sbin/init -o /var/log/wtmp -j WRITE

lidsconf -A -s /sbin/init -o /var/log/lastlog -j WRITE

lidsconf -A -s /sbin/halt -o /var/log/wtmp -j WRITE

lidsconf -A -s /sbin/halt -o /var/log/lastlog -j WRITE

lidsconf -A -s /etc/rc.d/rc.sysinit -o /var/log/wtmp -i 1 -j WRITE

lidsconf -A -s /etc/rc.d/rc.sysinit -o /var/log/lastlog -i 1 -j WRITE

Now, we set up access control for root's home folder. We allow only the bash history file to be appended:

f -A -o /root -j READONLY

lidsconf -A -s /bin/bash -o /root/.bash_history -j APPEND

Finally, we allow the init program to kill processes on shutdown:

lidsconf -A -s /sbin/init -o CAP_INIT_KILL -j GRANT

lidsconf -A -s /sbin/init -o CAP_KILL -j GRANT

Now, we allow fstab and init scripts to mount filesystems, kill processes and unmount filesystems:

lidsconf -A -s/etc/fstab -o CAP_SYS_ADMIN -j 1 -j GRANT

lidsconf -A -s /etc/rc.d/init.d/halt -o CAP_INIT_KILL -i 1 -j GRANT

lidsconf -A -s /etc/rc.d/init.d/halt -o CAP_KILL -i 1 -j GRANT

lidsconf -A -s /etc/rc.d/init.d/halt -o CAP_NET_ADMIN -i 1 -j GRANT

lidsconf -A -s /etc/rc.d/init.d/halt -o CAP_SYS_ADMIN -i 1 -j GRANT

Apache needs to have setuid and setgid capabilities. We also need to allow Apache to access log files and deny other applications from accessing the httpd binary:

lidsconf -A -s /usr/local/apache/bin/httpd -o CAP_SETUID -j GRANT

lidsconf -A -s /usr/local/apache/bin/httpd -o CAP_SETGID -j GRANT

lidsconf -A -o /etc/httpd -j DENY

lidsconf -A -s /usr/local/apache/bin/httpd -o /etc/httpd -j READONLY

lidsconf -A -o /usr/local/apache -j DENY

lidsconf -A -s /usr/local/apache/bin/httpd -o /usr/local/apache -j READONLY

lidsconf -A -o /var/log/httpd -j DENY

lidsconf -A -s /usr/local/apache/bin/httpd -o /var/log/httpd -j APPEND

lidsconf -A -s /usr/local/apache/bin/httpd -o /usr/local/apache/logs -j WRITE