Lance Spitzner

My commander used to tell me that to secure yourself against the enemy, you have to first know who your enemy is. This military doctrine readily applies to the world of network security. Just like the military, you have resources that you are trying to protect. To help protect these resources, you need to know who your threat is and how they are going to attack. This article does just that, it discusses the methodology and tools used by one of the most common and universal threats, the Script Kiddie.

Who is the Script Kiddie

The script kiddie is someone looking for the easy kill. They are not out for specific information or targeting a specific company. Their goal is to gain root the easiest way possible. They do this by focusing on a small number of exploits, and then searching the entire Internet for that exploit. Sooner or later they find someone vulnerable.

Some of them are advance users who develop their own tools and leave behind sophisticated backdoors. Others have no idea what they are doing and only know how to type "go" at the command prompt. Regardless of the their skill level, they all share a common strategy, randomly search for a specific weakness, then exploit that weakness.

The Threat

It is this random selection of targets that make the script kiddie such a dangerous threat. Sooner or later your systems and networks will be probed, you cannot hide from them. I know of admins who were amazed to have their systems scanned when they had been up for only two days, and no one knew about them. There is nothing amazing here. Most likely, their systems were scanned by a script kiddie who happened to be sweeping that network block.

If this was limited to several individual scans, statistics would be in your favor. With millions of systems on the Internet, odds are that no one would find you. However, this is not the case. Most of these tools are easy to use and widely distributed, anyone can use them. A rapidly growing number of people are obtaining these tools at an alarming rate. As the Internet knows no geographic bounds, this threat has quickly spread throughout the world. Suddenly, the law of numbers is turning against us. With so many users on the Internet using these tools, it is no longer a question of if, but when you will be probed.

This is an excellent example of why security through obscurity can fail you. You may believe that if no one knows about your systems, you are secure. Others believe that their systems are of no value, so why would anyone probe them? It is these very systems that the script kiddies are searching for, the unprotected system that is easy to exploit, the easy kill.

The Methodology

The script kiddie methodology is a simple one. Scan the Internet for a specific weakness, when you find it, exploit it. Most of the tools they use are automated, requiring little interaction. You launch the tool, then come back several days later to get your results.  No two tools are alike, just as no two exploits are alike. However, most of the tools use the same strategy. First, develop a database of IPs that can be scanned. Then, scan those IPs for a specific vulnerability.

For example, lets say a user had a tool that could exploit imap on Linux systems. First, they would develop a database of IP addresses that they could scan (i.e., systems that are up and reachable). Once this database of IP addresses is built, the user would want to determine which systems were running Linux. Many scanners today can easily determine this by sending bad packets to a system and seeing how they respond. Then, tools would be used to determine what Linux systems were running imap. All that is left now is to exploit those vulnerable systems.

You would think that all this scanning would be extremely noisy, attracting a great deal of attention. However, many people are not monitoring there systems, and do not realize they are being scanned. Also, many script kiddies quietly look for a single system they can exploit. Once they have exploited a system, they now use this systems as a launching pad. They can boldly scan the entire Internet without fear of retribution. If their scans are detected, the system admin and not the hacker will be held liable.

Also, these scan results are often archived or shared among other users, then used at a later date.  For example, a user develops a database of what ports are open on reachable Linux systems.  The user built this database to exploit the current imap vulnerability.  However, lets say that a month from now a new Linux exploit is identified on a different port.  Instead of having to build a new database (which is the most time consuming part), the user can quickly review his archived database and compromise the vulnerable systems.  As an alternative, script kiddies share or even buy databases of vulnerable systems from each other.  The script kiddie can then exploit your system without even scanning it.  Just because your systems have not been scanned recently does not mean you are secure.

The more sophisticated hackers implement trojans and backdoors once they compromise a system. Backdoors allow easy and unnoticed access to the system whenever the user wants. The trojans make the intruder undetectable. He would not show up in any of the logs, systems processes, or file structure. He builds a comfortable and safe home where he can blatantly scan the Internet.

These attacks are not limited to a certain time of the day. Many admins search their log entries for probes that happen late at night, believing this is when hackers attack. Script kiddies attack at any time. As they are scanning 24hrs a day, you have no idea when the probe will happen. Also, these attacks are launched throughout the world. Just as the Internet knows no geographical bounds, it knows no time zones. It may be midnight where the hacker is, but it is 1pm for you.

The Tools

The tools used are extremely simple in use. Most are limited to a single purpose with few options. First come the tools used to build an IP database. These tools are truly random, as they indiscriminently scan the Internet. For example, one tool has a single option, A, B, or C. The letter you select determines the size of the network to be scanned. The tool then randomly selects which IP network to scan. Another tool uses a domain name. The tools builds an IP database by conducting zone transfers of the domain name and all sub-domains. User'9s have built databases with over 2 million IPs by scanning the entire .com or .edu domain.

Once discovered, the IPs are then scanned by tools to determine vulnerabilities, such as the version of named, operating system, or services running on the system Once the vulnerable systems have been identified, the hacker strikes. Several tools exist that combine all these features together, simplifying the process even greater.

How to Protect Against This Threat

There are steps you can take to protect yourself against this threat. First, the script kiddie is going for the easy kill, they are looking for common exploits. Make sure your systems and networks are not vulnerable to these exploits. Both http://www.cert.org and http://www.ciac.org are excellent sources on what a common exploit is. Also, the listserv bugtraq is one of the best sources of information.

Another way to protect yourself is run only the services you need. If you do not need a service, turn it off. If you do need a service, make sure it is the latest version.  For examples on how to do this, check out my article Armoring Solaris.

As you learned from the tools section, DNS servers are often used to develop a database of systems that can be probed. Limit the systems that can conduct zone transfers from your Name Servers. Log any unauthorized zone transfers and follow up on them. I highly recommend upgrading to the latest version of BIND, which you can find at http://www.isc.org/bind.html.

Last, watch for your systems being probed. Once identified, you can track these probes and gain a better understanding of the threats to your network and react to these threats.

Conclusion

The script kiddie poses a threat to all systems. They show no bias and scan all systems, regardless of location and value. Sooner or later, your system will be probed. By understanding their motives and methods, you can better protect your systems against this threat.

NOTE:  Thanks to Brad Powell at Sun's Security Team for his help on this article