“Jailing is a mechanism to virtually change a system’s root
directory. By employing this method, administrators can isolate
services so that they cannot access the real filesystem structure.
You should run unsecured and sensitive network services in a chroot
jail, because if a hacker can break into a vulnerable service he
could exploit your whole system. If a service is jailed, the
intruder will be able to see only what you want him to see–that
is, nothing useful. Some of the most frequent targets of attack,
which therefore should be jailed, are BIND, Apache, FTP, and SSH.
SSHjail is a patch for the OpenSSH daemon. It modifies two OpenSSH
files (session.c and version.h) and allows you to jail your SSH
service without any need for SSH reconfiguration.“To use SSHjail you need the OpenSSH source package, the SSHjail
patch, and some development tools like patch and make. You also
need the OpenSSL and Zlib development libraries installed in order
to compile the patched SSH daemon. I’ve successfully installed
SSHjail on CentOS 4.2 and Fedora 6 distribution; the instructions
may be a bit different for your Linux flavor, but you’ll get the
idea…”