The
Tools and Methodologies of the Script Kiddie
Know Your Enemy
Lance
Spitzner
Last Modified: 15 February, 2000
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, the first of a three part series,
does just that, it discusses the tools and methodology used by one of the
most common and universal threats, the Script Kiddie. The
second paper focuses on how you can detect these attempts, identify what tools
they are using and what vulnerabilities they are looking for. The
third paper focuses on what happens once they gain root. Specifically,
how they cover their tracks and what they do next.
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, such as imapd_exploit.c.
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, such as Fyodor's nmap.
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 black-hat 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 black-hats
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 black-hats 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 black-hat is, but it is 1pm
for you.
This methodology of scanning for
vulnerable systems can be used for a variety of purposes. Recently,
new Denial of Service attacks have been reported, specifically DDoS (Distributed
Denial of Service attacks). These attacks are based on a single user
controlling hundreds, if not thousands of compromised systems throughout
the world. These compromised systems are then remotely coordinated
to execute Denial of Service attacks against a victim or victims.
Since multiple compromised systems are used, it is extremelly difficult
to defend against and identify the source of the attack. To gain
control of so many systems, script kiddie tactics are often employed.
Vulnerable systems are randomly identified and then compromised to be used
as DDoS launching pads. The more systems compromised, the more powerful
the DDoS attack. One example of such an attack is stacheldraht.
To learn more about Distributed Denial of Service attacks and how to protect
yourself, check out Paul Ferguson's site
Denialinfo
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 (z0ne is an excellent example of this).
The tools builds an IP database by conducting zone transfers of the domain
name and all sub-domains. User's 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 black-hat strikes. Several tools exist
that combine all these features together, simplifying the process even
greater, such as sscan
by jsbach or cracker.pl
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 www.cert.org
and www.ciac.org are excellent sources
on what a common exploit is. Also, the listserv bugtraq
(archived at securityfocus.com
)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 Armoring
Solaris , Armoring
Linux or Armoring
NT.
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 (software used for Domain
Name Service), which you can find at 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
Author's bio
Lance Spitzner enjoys learning by blowing up his Unix systems at
home. Before this, he was an Officer
in the Rapid Deployment Force, where he blew up things of a different
nature. You can reach him at lance@spitzner.net
.
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