1) Suppose that we locate a website in our machine, using Apache for example. Our site is designed for ten internal users, but we do not control this number. Subsequently, we consider making this system accessible on the Internet, as we think that it could be useful for the clients, and the only thing we have to do is assign a public IP address on the Internet to the system. What types of attack might this system suffer?
2) How can we detect the files with suid in our system? Which commands are necessary? And the directories with SUID or SGID? Why is it necessary, for example, for /usr/bin/passwd to have a SUID bit?
3) The .rhosts files, as we have seen, are a significant danger for security. Could we use some type of automatic method for regularly checking these files? How?
4) Let us suppose that we want to disable a service that we know has its /etc/init.d/service script that controls it: we wish to disable it in all the runlevels in which it appears. How do we find the runlevels in which it is present? (for example, searching for links to the script).
5) Examine the active services in your machine. Are they all necessary? How would we protect or deactivate them?
6) Practice using some of the described security tools (nmap, nessus etc.).
7) Which IPtables rules would be necessary for a machine that we only wish to access through SSH from a specific address?
8) What if we only want to access the web server?