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Chapter: Security in Computing : Security in Networks

Who Attacks Networks?

Who are the attackers? We cannot list their names, just as we cannot know who are all the criminals in our city, country, or the world. Even if we knew who they were, we do not know if we could stop their behavior.

Who Attacks Networks?


Who are the attackers? We cannot list their names, just as we cannot know who are all the criminals in our city, country, or the world. Even if we knew who they were, we do not know if we could stop their behavior.  To have some idea of who the attackers might be, we return to concepts introduced in Chapter 1, where we described the three necessary components of an attack: method, opportunity, and motive.


In the next sections we explore method: tools and techniques the attackers use. Here we consider first the motives of attackers. Focusing on motive may give us some idea of who might attack a networked host or user. Four important motives are challenge or power, fame, money, and ideology.




Why do people do dangerous or daunting things, like climb mountains or swim the English Channel or engage in extreme sports? Because of the challenge. The situation is no different for someone skilled in writing or using programs. The single most significant motivation for a network attacker is the intellectual challenge. He or she is intrigued with knowing the answers to Can I defeat this network? What would happen if I tried this approach or that technique?


Some attackers enjoy the intellectual stimulation of defeating the supposedly undefeatable. For example, Robert Morris, who perpetrated the Internet worm in 1988 (described in Chapter 3), attacked supposedly as an experiment to see if he could exploit a particular vulnerability. Other attackers, such as the Cult of the Dead Cow, seek to demonstrate weaknesses in security defenses so that others will pay attention to strengthening security. Still other attackers are unnamed, unknown individuals working persistently just to see how far they can go in performing unwelcome activities.


However, as you will soon see, only a few attackers find previously unknown flaws. The vast majority of attackers repeat well-known and even well-documented attacks, sometimes only to see if they work against different hosts. In these cases, intellectual stimulation is certainly not the driving force, when the attacker is merely pressing [run] to activate an attack discovered, designed, and implemented by someone else.



The challenge of accomplishment is enough for some attackers. But other attackers seek recognition for their activities. That is, part of the challenge is doing the deed; another part is taking credit for it. In many cases, we do not know who the attackers really are, but they leave behind a "calling card" with a name or moniker: Mafiaboy, Kevin Mitnick, Fluffy Bunny, and members of the Chaos Computer Club, for example. The actors often retain some anonymity by using pseudonyms, but they achieve fame nevertheless. They may not be able to brag too openly, but they enjoy the personal thrill of seeing their attacks written up in the news media.


Money and Espionage


As in other settings, financial reward motivates attackers, too. Some attackers perform industrial espionage, seeking information on a company's products, clients, or long-range plans. We know industrial espionage has a role when we read about laptops and sensitive papers having been lifted from hotel rooms when other more valuable items were left behind. Some countries are notorious for using espionage to aid their state-run industries.


Sometimes industrial espionage is responsible for seemingly strange corporate behavior. For example, in July 2002, newspapers reported that a Yale University security audit had revealed that admissions officers from rival Princeton University broke into Yale's online admissions notification system. The Princeton snoops admitted looking at the confidential decisions about eleven students who had applied to both schools but who had not yet been told of their decisions by Yale. In another case, a startup company was about to activate its first application on the web. Two days before the application's unveiling, the head offices were burglarized. The only item stolen was the one computer containing the application's network design. Corporate officials had to make a difficult choice: Go online knowing that a competitor might then take advantage of knowing the internal architecture or delay the product's rollout until the network design was changed. They chose the latter. Similarly, the chief of security for a major manufacturing company has reported privately to us of evidence that one of the company's competitors had stolen information. But he could take no action because he could not determine which of three competitors was the actual culprit.


Industrial espionage is illegal, but it occurs, in part because of the high potential gain. Its existence and consequences can be embarrassing for the target companies. Thus, many incidents go unreported, and there are few reliable statistics on how much industrial espionage and "dirty tricks" go on. Yearly since 1997, the Computer Security Institute and the U.S. Federal Bureau of Investigation have surveyed security professionals from companies, government agencies, universities, and organizations, asking them to report perceptions of computer incidents. About 500 responses are received for each survey. Theft of intellectual property amounted to a total loss of $31 million, with an average loss per incident of $350 thousand, making this the category of third-highest loss. That amount was more than double the amount reported in the 2004 survey. (These survey results are anecdotal, so it is hard to draw many conclusions. For full details on the survey see [CSI05].) Industrial espionage, leading to loss of intellectual property, is clearly a problem.


Organized Crime


With the growth in commercial value of the Internet, participation by organized crime has also increased. In October 2004, police arrested members of a 28-person gang of Internet criminals, called the Shadowcrew, who operated out of six foreign countries and eight states in the United States. Six leaders of that group pled guilty to charges, closing an illicit business that trafficked in at least 1.5 million stolen credit and bank card numbers and resulted in losses in excess of $4 million. In July 2003, Alexey Ivanov was convicted as the supervisor of a wide-ranging, organized criminal enterprise that engaged in sophisticated manipulation of computer data, financial information, and credit card numbers. Ivanov and group were responsible for an aggregate loss of approximately $25 million. And in January 2006, Jeanson James Ancheta pled guilty to having infected 400,000 computers with malicious code and renting their use to others to use to launch attacks on others. In June 2005, the FBI and law enforcement from 10 other countries conducted over 90 searches worldwide as part of "Operation Site Down," designed to disrupt and dismantle many of the leading criminal organizations that illegally distribute and trade in copyrighted software, movies, music, and games on the Internet [DOJ06]. Brazilian police arrested 85 people in 2005 for Internet fraud.


Although money is common to these crimes, the more interesting fact is that they often involve collaborators from several countries. These more sophisticated attacks require more than one person working out of a bedroom, and so organization and individual responsibilities follow. With potential revenue in the millions of dollars and operations involving hundreds of thousands of credit card numbers and other pieces of identity, existing organized crime units are sure to take notice. As Williams [WIL01] says, "[T]here is growing evidence that organized crime groups are exploiting the new opportunities offered by the Internet."




In the last few years, we are starting to find cases in which attacks are perpetrated to advance ideological ends. For example, many security analysts believe that the Code Red worm of 2001 was launched by a group motivated by the tension in U.S.China relations. Denning [DEN99a] has distinguished between two types of related behaviors, hactivism and cyberterrorism. Hactivism involves "operations that use hacking techniques against a target's [network] with the intent of disrupting normal operations but not causing serious damage." In some cases, the hacking is seen as giving voice to a constituency that might otherwise not be heard by the company or government organization. For example, Denning describes activities such as virtual sit-ins, in which an interest group floods an organization's web site with traffic to demonstrate support of a particular position. Cyberterrorism is more dangerous than hactivism: "politically motivated hacking operations intended to cause grave harm such as loss of life or severe economic damage."


Security and terrorism experts are seeing increasing use of the Internet as an attack vector, as a communications medium among attackers, and as a point of attack. Cullison [CUL04] presents a very interesting insight (which we overview in Sidebar 1-6, p. 24) into of the use of technology by al Qaeda.




Now that we have listed many motives for attacking, we turn to how attackers perpetrate their attacks. Attackers do not ordinarily sit down at a terminal and launch an attack. A clever attacker investigates and plans before acting. Just as you might invest time in learning about a jewelry store before entering to steal from it, a network attacker learns a lot about a potential target before beginning the attack. We study the precursors to an attack so that if we can recognize characteristic behavior, we may be able to block the attack before it is launched.


Because most vulnerable networks are connected to the Internet, the attacker begins preparation by finding out as much as possible about the target. An example of information gathering is given in [HOB97]. (Not all information gathered is accurate, however; see Sidebar 7-4 for a look at reconnaissance combined with deception.)


Port Scan


An easy way to gather network information is to use a port scan, a program that, for a particular IP address, reports which ports respond to messages and which of several known vulnerabilities seem to be present. Farmer and Venema [FAR93] are among the first to describe the technique.


A port scan is much like a routine physical examination from a doctor, particularly the initial questions used to determine a medical history. The questions and answers by themselves may not seem significant, but they point to areas that suggest further investigation.


Port scanning tells an attacker three things: which standard ports or services are running and responding on the target system, what operating system is installed on the target system, and what applications and versions of applications are present. This information is readily available for the asking from a networked system; it can be obtained quietly, anonymously, without identification or authentication, drawing little or no attention to the scan.


Port scanning tools are readily available, and not just to the underground community. The nmap scanner by Fyodor at www.insecure.org/nmap is a useful tool that anyone can download. Given an address, nmap will report all open ports, the service they support, and the owner (user ID) of the daemon providing the service. (The owner is significant because it implies what privileges would descend upon someone who compromised that service.) Another readily available scanner is netcat, written by Hobbit, at www.l0pht.com/users/l0pht. (That URL is "letter ell," "digit zero," p-h-t.) Commercial products are a little more costly, but not prohibitive. Well-known commercial scanners are Nessus (Nessus Corp. [AND03]), CyberCop Scanner (Network Associates), Secure Scanner (Cisco), and Internet Scanner (Internet Security Systems).


Social Engineering


The port scan gives an external picture of a networkwhere are the doors and windows, of what are they constructed, to what kinds of rooms do they open? The attacker also wants to know what is inside the building. What better way to find out than to ask?


Suppose, while sitting at your workstation, you receive a phone call. "Hello, this is John Davis from IT support. We need to test some connections on the internal network. Could you please run the command ipconfig/all on your workstation and read to me the addresses it displays?" The request sounds innocuous. But unless you know John Davis and his job responsibilities well, the caller could be an attacker gathering information on the inside architecture.


Social engineering involves using social skills and personal interaction to get someone to reveal security-relevant information and perhaps even to do something that permits an attack. The point of social engineering is to persuade the victim to be helpful. The attacker often impersonates someone inside the organization who is in a bind: "My laptop has just been stolen and I need to change the password I had stored on it," or "I have to get out a very important report quickly and I can't get access to the following thing." This attack works especially well if the attacker impersonates someone in a high position, such as the division vice president or the head of IT security. (Their names can sometimes be found on a public web site, in a network registration with the Internet registry, or in publicity and articles.) The attack is often directed at someone low enough to be intimidated or impressed by the high-level person. A direct phone call and expressions of great urgency can override any natural instinct to check out the story.


Because the victim has helped the attacker (and the attacker has profusely thanked the victim), the victim will think nothing is wrong and not report the incident. Thus, the damage may not be known for some time.


An attacker has little to lose in trying a social engineering attack. At worst it will raise awareness of a possible target. But if the social engineering is directed against someone who is not skeptical, especially someone not involved in security management, it may well succeed. We as humans like to help others when asked politely.




From a port scan the attacker knows what is open. From social engineering, the attacker knows certain internal details. But a more detailed floor plan would be nice. Intelligence is the general term for collecting information. In security it often refers to gathering discrete bits of information from various sources and then putting them together like the pieces of a puzzle.


One commonly used intelligence technique is called "dumpster diving." It involves looking through items that have been discarded in rubbish bins or recycling boxes. It is amazing what we throw away without thinking about it. Mixed with the remains from lunch might be network diagrams, printouts of security device configurations, system designs and source code, telephone and employee lists, and more. Even outdated printouts may be useful. Seldom will the configuration of a security device change completely. More often only one rule is added or deleted or modified, so an attacker has a high probability of a successful attack based on the old information.


Gathering intelligence may also involve eavesdropping. Trained spies may follow employees to lunch and listen in from nearby tables as coworkers discuss security matters. Or spies may befriend key personnel in order to co-opt, coerce, or trick them into passing on useful information.


Most intelligence techniques require little training and minimal investment of time. If an attacker has targeted a particular organization, spending a little time to collect background information yields a big payoff.


Operating System and Application Fingerprinting


The port scan supplies the attacker with very specific information. For instance, an attacker can use a port scan to find out that port 80 is open and supports HTTP, the protocol for transmitting web pages. But the attacker is likely to have many related questions, such as which commercial server application is running, what version, and what the underlying operating system and version are. Once armed with this additional information, the attacker can consult a list of specific software's known vulnerabilities to determine which particular weaknesses to try to exploit.


How can the attacker answer these questions? The network protocols are standard and vendor independent. Still, each vendor's code is implemented independently, so there may be minor variations in interpretation and behavior. The variations do not make the software noncompliant with the standard, but they are different enough to make each version distinctive. For example, each version may have different sequence numbers, TCP flags, and new options. To see why, consider that sender and receiver must coordinate with sequence numbers to implement the connection of a TCP session. Some implementations respond with a given sequence number, others respond with the number one greater, and others respond with an unrelated number. Likewise, certain flags in one version are undefined or incompatible with others. How a system responds to a prompt (for instance, by acknowledging it, requesting retransmission, or ignoring it) can also reveal the system and version. Finally, new features offer a strong clue: A new version will implement a new feature but an old version will reject the request. All these peculiarities, sometimes called the operating system or application fingerprint, can mark the manufacturer and version.


For example, in addition to performing its port scan, a scanner such as nmap will respond with a guess at the target operating system. For more information about how this is done, see the paper at www.insecure.org/nmap/nmap-fingerprinting-article.html.


Sometimes the application identifies itself. Usually a client-server interaction is handled completely within the application according to protocol rules: "Please send me this page; OK but run this support code; thanks, I just did." But the application cannot respond to a message that does not follow the expected form. For instance, the attacker might use a Telnet application to send meaningless messages to another application. Ports such as 80 (HTTP), 25 (SMTP), 110 (POP), and 21 (FTP) may respond with something like


Server: Netscape-Commerce/1.12


Your browser sent a non-HTTP compliant message.





Microsoft ESMTP MAIL Service, Version: 5.0.2195.3779



This reply tells the attacker which application and version are running.


Bulletin Boards and Chats


The Internet is probably the greatest tool for sharing knowledge since the invention of the printing press. It is probably also the most dangerous tool for sharing knowledge.


Numerous underground bulletin boards and chat rooms support exchange of information. Attackers can post their latest exploits and techniques, read what others have done, and search for additional information on systems, applications, or sites. Remember that, as with everything on the Internet, anyone can post anything, so there is no guarantee that the information is reliable or accurate. And you never know who is reading from the Internet. (See Sidebar 7-4 on law enforcement officials' "going underground" to catch malicious hackers.)


Availability of Documentation


The vendors themselves sometimes distribute information that is useful to an attacker. For example, Microsoft produces a resource kit by which application vendors can investigate a Microsoft product in order to develop compatible, complementary applications. This toolkit also gives attackers tools to use in investigating a product that can subsequently be the target of an attack.


Reconnaissance: Concluding Remarks


A good thief, that is, a successful one, spends time understanding the context of the target. To prepare for perpetrating a bank theft, the thief might monitor the bank, seeing how many guards there are, when they take breaks, when cash shipments arrive, and so forth.


Remember that time is usually on the side of the attacker. In the same way that a bank might notice someone loitering around the entrance, a computing site might notice exceptional numbers of probes in a short time. But the clever thief or attacker will collect a little information, go dormant for a while, and resurface to collect more. So many people walk past banks and peer in the windows, or scan and probe web hosts that individual peeks over time are hard to correlate.


The best defense against reconnaissance is silence. Give out as little information about your site as possible, whether by humans or machines.

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