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Maximum Security:

A Hacker's Guide to Protecting Your Internet Site and Network

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The Remote Attack

In this chapter, I will examine the remote attack. I will define what such an attack is and demonstrate some key techniques employed. Moreover, this chapter will serve as a generalized primer for new system administrators, who may have never encountered the remote attack in real life.

The purpose of this chapter is to begin integrating the information that has already been offered to this point. In other words, it is time to put the pieces together.

What Is a Remote Attack?

A remote attack is any attack that is initiated against a machine that the attacker does not currently have control over; that is, it is an attack against any machine other than the attacker's own (whether that machine is on the attacker's subnet or 10,000 miles away). The best way to define a remote machine is this:

A remote machine is any machine--other than the one you are now on--that can be reached through some protocol over the Internet or any other network or medium.

The First Steps

The first steps, oddly enough, do not involve much contact with the target. (That is, they won't if the cracker is smart.) The cracker's first problem (after identifying the type of network, the target machines, and so on) is to determine with whom he is dealing. Much of this information can be acquired without disturbing the target. (We will assume for now that the target does not run a firewall. Most networks do not. Not yet, anyway.) Some of this information is gathered through the following techniques:

  • Running a host query. Here, the cracker gathers as much information as is currently held on the target in domain servers. Such a query may produce volumes of information (remember the query on Boston University in Chapter 9, "Scanners"?) or may reveal very little. Much depends on the size and the construct of the network.

  • For example, under optimal circumstances of examining a large and well-established target, this will map out the machines and IPs within the domain in a very comprehensive fashion. The names of these machines may give the cracker a clue as to what names are being used in NIS (if applicable). Equally, the target may turn out to be a small outfit, with only two machines; in that case, the information will naturally be sparse. It will identify the name server and the IPs of the two boxes (little more than one could get from a WHOIS query). One interesting note is that the type of operating system can often be discerned from such a query.

  • A WHOIS query. This will identify the technical contacts. Such information may seem innocuous. It isn't. The technical contact is generally the person at least partially responsible for the day-to-day administration of the target. That person's e-mail address will have some value. (Also, between this and the host query, you can determine whether the target is a real box, a leaf node, a virtual domain hosted by another service, and so on.)

  • Running some Usenet and Web searches. There are a number of searches the cracker might want to conduct before actually coming into contact with the target. One is to run the technical contact's name through a search engine (using a forced, case-sensitive, this-string-only conditional search). The cracker is looking to see if the administrators and technical contacts sport much traffic in Usenet. Similarly, this address (or addresses) should be run through searchable archives of all applicable security mailing lists.

The techniques mentioned in this list may seem superfluous until you understand their value. Certainly, Farmer and Venema would agree on this point:

What should you do? First, try to gather information about your (target) host. There is a wealth of network services to look at: finger, showmount, and rpcinfo are good starting points. But don't stop there--you should also utilize DNS, whois, sendmail (smtp), ftp, uucp, and as many other services as you can find.

Cross Reference: The preceding paragraph is excerpted from Improving the Security of Your Site by Breaking Into It by Dan Farmer and Wietse Venema. It can be found online at

Collecting information about the system administrator is paramount. A system administrator is usually responsible for maintaining the security of a site. There are instances where the system administrator may run into problems, and many of them cannot resist the urge to post to Usenet or mailing lists for answers to those problems. By taking the time to run the administrator's address (and any variation of it, as I will explain in the next section), you may be able to gain greater insight into his network, his security, and his personality. Administrators who make such posts typically specify their architecture, a bit about their network topology, and their stated problem.

Even evidence of a match for that address (or lack thereof) can be enlightening. For example, if a system administrator is in a security mailing list or forum each day, disputing or discussing various security techniques and problems with fellow administrators, this is evidence of knowledge. In other words, this type of person knows security well and is therefore likely well prepared for an attack. Analyzing such a person's posts closely will tell you a bit about his stance on security and how he implements it. Conversely, if the majority of his questions are rudimentary (and he often has a difficult time grasping one or more security concepts), it might be evidence of inexperience.

From a completely different angle, if his address does not appear at all on such lists or in such forums, there are only a few possibilities why. One is that he is lurking through such groups. The other is that he is so bad-ass that he has no need to discuss security at all. (Basically, if he is on such lists at all, he DOES receive advisories, and that is, of course, a bad sign for the cracker, no matter what way you look at it. The cracker has to rely in large part on the administrator's lack of knowledge. Most semi-secure platforms can be relatively secure even with a minimal effort by a well-trained system administrator.)

In short, these searches make a quick (and painless) attempt to cull some important information about the folks at the other end of the wire.

You will note that I referred to "any variation" of a system administrator's address. Variations in this context mean any possible alternate addresses. There are two kinds of alternate addresses. The first kind is the individual's personal address. That is, many system administrators may also have addresses at or on networks other than their own. (Some administrators are actually foolish enough to include these addresses in the fields provided for address on an InterNIC record.) So, while they may not use their work address to discuss (or learn about) security, it is quite possible that they may be using their home address.

To demonstrate, I once cracked a network located in California. The administrator of the site had an account on AOL. The account on AOL was used in Usenet to discuss various security issues. By following this man's postings through Usenet, I was able to determine quite a bit. In fact (and this is truly extraordinary), his password, I learned, was the name of his daughter followed by the number 1.

The other example of a variation of an address is this: either the identical address or an address assigned to that person's same name on any machine within his network. Now, let's make this a little more clear. First, on a network that is skillfully controlled, no name is associated with root. That is because root should be used as little as possible and viewed as a system ID, not to be invoked unless absolutely necessary. (In other words, because su and perhaps other commands or devices exist that allow an administrator to do his work, root need not be directly invoked, except in a limited number of cases.)

NOTE: Attacking a network run on Windows NT is a different matter. In those cases, you are looking to follow root (or rather, Administrator) on each box. The design of NT makes this a necessity, and Administrator on NT is vastly different from root on a UNIX box.

Because root is probably not invoked directly, the system administrator's ID could be anything. Let's presume here that you know that ID. Let's suppose it is walrus. Let us further suppose that on the host query that you conducted, there are about 150 machines. Each of those machines has a distinct name. For example, there might be,,,, and so forth. (Although, in practice, they will more likely have "theme" names that obscure what the machine actually does, like,, and

The cracker should try the administrator's address on each machine. Thus, he will be trying,, and so forth. (This is what I refer to as a variation on a target administrator's address.) In other words, try this on each box on the network, as well as run all the general diagnostic stuff on each of these machines. Perhaps walrus has a particular machine that he favors, and it is from this machine that he does his posting.

Here's an interesting note: If the target is a provider (or other system that one can first gain legitimate access to), you can also gain an enormous amount of information about the system administrator simply by watching where he is coming in from. This, to some extent, can be done from the outside as well, with a combination of finger and rusers. In other words, you are looking to identify foreign networks (that is, networks other than the target) on which the system administrator has accounts. Obviously, if his last login was from Netcom, he has an account on Netcom. Follow that ID for a day or so and see what surfaces.

About Finger Queries

In the previously referenced paper by Farmer and Venema (a phenomenal and revolutionary document in terms of insight), one point is missed: The use of the finger utility can be a dangerous announcement of your activities. What if, for example, the system administrator is running MasterPlan?

TIP: MasterPlan is a utility I discuss in Chapter 13, "Techniques to Hide One's Identity." Its function is to trap and log all finger queries directed to the user; that is, MasterPlan will identify the IP of the party doing the fingering, the time that such fingering took place, the frequency of such fingering, and so forth. It basically attempts to gather as much information about the person fingering you as possible. Also, it is not necessary that they use MasterPlan. The system administrator might easily have written his own hacked finger daemon, one that perhaps even traces the route back to the original requesting party--or worse, fingers them in return.

To avoid the possibility of their finger queries raising any flags, most crackers use finger gateways. Finger gateways are Web pages, and they usually sport a single input field that points to a CGI program on the drive of the remote server that performs finger lookup functions. In Figure 25.1, I have provided an example of one such finger gateway. (This one is located at the University of Michigan Medical Center.)

FIGURE 25.1.
An example of a finger gateway at the University of Michigan.

By using a finger gateway, the cracker can obscure his source address. That is, the finger query is initiated by the remote system that hosts the finger gateway. (In other words, not the cracker's own machine but some other machine.) True, an extremely paranoid system administrator might track down the source address of that finger gateway; he might even contact the administrator of the finger gateway site to have a look at the access log there. In this way, he could identify the fingering party. That this would happen, however, is quite unlikely, especially if the cracker staggers his gateways. In other words, if the cracker intends to do any of this type of work "by hand," he should really do each finger query from a different gateway. Because there are 3,000+ finger gateways currently on the Web, this is not an unreasonable burden. Furthermore, if I were doing the queries, I would set them apart by several minutes (or ideally, several hours).

NOTE: One technique involves the redirection of a finger request. This is where the cracker issues a raw finger request to one finger server, requesting information from another. This is referred to as forwarding a finger request. The syntax of such a command is finger For example, if you wanted to finger a user at, you might use's finger service to forward the request. However, in today's climate, most system administrators have finger forwarding turned off.

The Operating System

You may have to go through various methods (including but not limited to those described in the preceding section) to identify the operating system and version being used on the target network. In earlier years, one could be pretty certain that the majority of machines on a target network ran similar software on similar hardware. Today, it is another ball game entirely. Today, networks may harbor dozens of different machines with disparate operating systems and architecture. One would think that for the cracker, this would be a hostile and difficult-to-manage environment. Not so.

The more diverse your network nodes are (in terms of operating system and architecture), the more likely it is that a security hole exists. There are reasons for this, and while I do not intend to explain them thoroughly, I will relate at least this: Each operating system has its own set of bugs. Some of these bugs are known, and some may be discovered over time. In a relatively large network, where there may be many different types of machines and software, you have a better chance of finding a hole. The system administrator is, at day's end, only a human being. He cannot be constantly reviewing security advisories for each platform in turn. There is a strong chance that his security knowledge of this or that system is weak.

In any event, once having identified the various operating systems and architectures available at the target, the next step is study. A checklist should be made that lists each operating system and machine type. This checklist will assist you tremendously as you go to the next step, which is to identify all known holes on that platform and understand each one.

NOTE: Some analysts might make the argument that tools like ISS and SATAN will identify all such holes automatically and, therefore, research need not be done. This is erroneous, for several reasons. First, such tools may not be complete in their assessment. Here is why: Although both of the tools mentioned are quite comprehensive, they are not perfect. For example, holes emerge each day for a wide range of platforms. True, both tools are extensible, and one can therefore add new scan modules, but the scanning tools that you have are limited to the programmer's knowledge of the holes that existed at the time of the coding of the application.

Therefore, to make a new scanning module to be added to these extensible and malleable applications, you must first know that such new holes exist. Second, and perhaps more importantly, simply knowing that a hole exists does not necessarily mean that you can exploit it--you must first understand it. (Unless, of course, the hole is an obvious and self-explanatory one, such as the -froot rlogin problem on some versions of the AIX operating system. By initiating an rlogin session with the -froot flags, you can gain instant privileged access on many older AIX-based machines.) For these reasons, hauling off and running a massive scan is a premature move.

To gather this information, you will need to visit a few key sites. The first such site you need to visit is the firewalls mailing list archive page.

Cross Reference: The firewalls mailing list archive page can be found online at

You may initially wonder why this list would be of value, because the subject discussed is firewall-related. (Remember, we began this chapter with the presumption that the target was not running a firewall.) The firewalls list archive is valuable because it is often used--over the objections of many list members--to discuss other security-related issues. Another invaluable source of such data is BUGTRAQ, which is a searchable archive of known vulnerabilities on various operating systems (though largely UNIX.)

Cross Reference: BUGTRAQ is located online at

These searchable databases are of paramount importance. A practical example will help tremendously at this point. Suppose that your target is a machine running AIX. First, you would go to the ARC Searchable WAIS Gateway for DDN and CERT advisories.

Cross Reference: The ARC Searchable WAIS Gateway for DDN and CERT advisories can be found online at

Figure 25.2 shows how the WAIS gateway at this site is configured.

FIGURE 25.2.
The WAIS gateway at
ARC.COM for searching security advisories.

At the bottom of that page is an input field. Into it, I entered the search term AIX. The results of that search produced a laundry list of AIX vulnerabilities. (See Figure 25.3.)

FIGURE 25.3.
A laundry list of AIX vulnerabilities from the WAIS gateway.

At this stage, you can begin to do some research. After reading the initial advisory, if there is no more information than a simple description of the vulnerability, do not despair. You just have to go to the next level. The next phase is a little bit more complex. After identifying the most recent weakness (and having read the advisory), you must extract from that advisory (and all that follow it) the commonly used, often abbreviated, or "jargon," name for the hole. For example, after a hole is discovered, it is often referred to by security folks with a name that may not reflect the entire problem. (An example would be "the Linux telnetd problem" or "AIX's froot hole" or some other, brief term by which the hole becomes universally identified.) The extraction process is quickly done by taking the ID number of the advisory and running it through one of the abovementioned archives like BUGTRAQ or Firewalls. Here is why:

Typically, when a security professional posts either an exploit script, a tester script (tests to see if the hole exists) or a commentary, they will almost always include complete references to the original advisory. Thus, you will see something similar to this in their message: Here's a script to test if you are vulnerable to the talkd problem talked about in CA-97.04..

This message is referring to CERT Advisory number 97.04, which was first issued on January 27, 1997. By using this number as a search expression, you will turn up all references to it. After reading 10 or 12 results from such a search, you will know what the security crowd is calling that hole. After you have that, you can conduct an all-out search in all legitimate and underground database sources to get every shred of information about the hole. You are not looking for initial postings in particular, but subsequent, trailing ones. (Some archives have an option where you can specify a display by thread; these are preferred. This allows you to see the initial posting and all subsequent postings about that original message; that is, all the "re:" follow-ups.) However, some search engines do not provide for an output in threaded form; therefore, you will simply have to rake through them by hand.

The reason that you want these follow-ups is because they usually contain exploit or test scripts (programs that automatically test or simulate the hole). They also generally contain other technical information related to the hole. For example, one security officer might have found a new way to implement the vulnerability, or might have found that an associated program (or include file or other dependency) may be the real problem or even a great contributor to the hole. The thoughts and reflections of these individuals are pure gold, particularly if the hole is a new one. These individuals are actually doing all the work for you: analyzing and testing the hole, refining attacks against it, and so forth.

TIP: Many exploit and test scripts are posted in standard shell or C language and are therefore a breeze to either reconfigure for your own system or compile for your architecture. In most instances, only minimal work has to be done to make them work on your platform.

So, to this point, you have defined a portion (or perhaps all) of the following chief points:

  • Who the administrator is

  • The machines on the network, and perhaps their functions and domain servers

  • Their operating systems

  • Their probable holes

  • Any discussion by the administrator about the topology, management, policies, construction, or administration of the network

Now you can proceed to the next step.

One point of interest: It is extremely valuable if you can also identify machines that may be co-located. This is, of course, strictly in cases where the target is an Internet service provider (ISP). ISPs often offer deals for customers to co-locate a machine on their wire. There are certain advantages to this for the customer. One of them is cost. If the provider offers to co-locate a box on its T3 for, say, $600 a month, this is infinitely less expensive than running a machine from your own office that hooks into a T1. A T1 runs about $900-$1,200 monthly. You can see why co-location is popular: You get speeds far faster for much less money and headache. For the ISP, it is nothing more than plugging a box into its Ethernet system. Therefore, even setup and administration costs are lower. And, perhaps most importantly of all, it takes the local telephone company out of the loop. Thus, you cut even more cost, and you can establish a server immediately instead of waiting six weeks.

These co-located boxes may or may be not be administrated by the ISP. If they are not, there is an excellent chance that these boxes may either have (or later develop) holes. This is especially likely if the owner of the box employs a significant amount of CGI or other self-designed program modules that the ISP has little or no control over. By compromising that box, you have an excellent chance of bringing the entire network under attack, unless the ISP has purposefully strung the machine directly to its own router, a hub (or instituted some other procedure of segmenting the co-located boxes from the rest of the network.)

NOTE: This can be determined to some degree using traceroute or whois services. In the case of traceroute, you can identify the position of the machine on the wire by examining the path of the traced route. In a whois query, you can readily see whether the box has its own domain server or whether it is using someone else's (an ISP's).

Doing a Test Run

The test-run portion of the attack is practical only for those individuals who are serious about cracking. Your average cracker will not undertake such activity, because it involves spending a little money. However, if I were counseling a cracker, I would recommend it.

This step involves establishing a single machine with the identical distribution as the target. Thus, if the target is a SPARCstation 2 running Solaris 2.4, you would erect an identical machine and string it to the Net via any suitable method (by modem, ISDN, Frame Relay, T1, or whatever you have available). After you have established the machine, run a series of attacks against it. There are two things you are looking for:

  • What the attacks are going to look like from the attacking side

  • What the attacks will look like from the victim's side

There are a number of reasons for this, and some are not so obvious. In examination of the logs on the attacking side, the cracker can gain an idea of what the attack should look like if his target is basically unprotected--in other words, if the target is not running custom daemons. This provides the cracker a little road map to go by; certainly, if his ultimate scan and attack of the target do not look nearly identical, this is cause for concern. All things being equal, an identically configured machine (or, I should say, an apparently identically configured machine) should respond identically. If it does not, the folks at the target have something up their sleeve. In this instance, the cracker would be wise to tread carefully.

By examining the victim-side logs, the cracker can get a look at what his footprint will look like. This is also important to know. On diverse platforms, there are different logging procedures. The cracker should know at a minimum exactly what these logging procedures are; that is, he needs to know each and every file (on the identically configured machine) that will show evidence of an intrusion. This information is paramount, because it serves as a road map also: It shows him exactly what files have to be altered to erase any evidence of his attack. The only way to identify these files for certain is to conduct a test under a controlled environment and examine the logs for themselves.

In actual attacks, there should be only a few seconds (or minutes at most) before root (or some high level of privilege) is obtained. Similarly, it should be only seconds thereafter (or minutes at worst) before evidence of that intrusion is erased. For the cracker, any other option is a fatal one. They may not suffer from it in the short run, but in the long run, they will end up in handcuffs.

This step is not as expensive as you would think. There are newsgroups (most notably, where one can obtain the identical machine (or a close facsimile) for a reasonable price. Generally, the seller of such a machine will load a full version of the operating system "for testing purposes only." This is their way of saying "I will give you the operating system, which comes without a license and therefore violates the license agreement. If you keep it and later come under fire from the vendor, you are on your own."

Even licensed resellers will do this, so you can end up with an identical machine without going to too much expense. (You can also go to defense contracting firms, many of which auction off their workstations for a fraction of their fair market value. The only bar here is that you must have the cash ready; you generally only get a single shot at a bid.)

Other possibilities include having friends set up such a box at their place of work or even at a university. All you really need are the logs. I have always thought that it would be a good study practice to maintain a database of such logs per operating system per attack and per scanner--in other words, have a library of what such attacks look like, given the aforementioned variables. This, I think, would be a good training resource for new system administrators, something like "This is what a SS4 looks like when under attack by someone using ISS. These are the log files you need to look for and this is how they will appear."

Surely, a script could be fashioned (perhaps an automated one) that would run a comparative analysis against the files on your workstation. This process could be done once a day as a cron job. It seems to me that at least minimal intrusion-detection systems could be designed this way. Such tools do exist, but have been criticized by many individuals because they can be "fooled" too easily. There is an excellent paper that treats this subject, at least with respect to SunOS. It is titled USTAT: A Real Time Intrusion Detection System for UNIX. (This paper was, in fact, a thesis for the completion of a master's in computer science at the University of Santa Barbara, California. It is very good.) In the abstract, the author writes:

In this document, the development of the first USTAT prototype, which is for SunOS 4.1.1, is described. USTAT makes use of the audit trails that are collected by the C2 Basic Security Module of SunOS, and it keeps track of only those critical actions that must occur for the successful completion of the penetration. This approach differs from other rule-based penetration identification tools that pattern match sequences of audit records.

Cross Reference: The preceding paragraph is excerpted from USTAT: A Real Time Intrusion Detection System for UNIX by Koral Ilgun. It can be found online at

Although we proceeded under the assumption that the target network was basically an unprotected, out-of-the-box install, I thought I should mention tools like the one described in the paper referenced previously. The majority of such tools have been employed on extremely secure networks--networks often associated with classified or even secret or top-secret work.

Another interesting paper lists a few of these tools and makes a brief analysis of each. It discusses how

Computer security officials at the system level have always had a challenging task when it comes to day-to-day mainframe auditing. Typically the auditing options/features are limited by the mainframe operating system and other system software provided by the hardware vendor. Also, since security auditing is a logical subset of management auditing, some of the available auditing options/features may be of little value to computer security officials. Finally, the relevant auditing information is probably far too voluminous to process manually and the availability of automated data reduction/analysis tools is very limited. Typically, 95% of the audit data is of no security significance. The trick is determining which 95% to ignore.

Cross Reference: The previous paragraph is excerpted from Summary of the Trusted Information Systems (TIS) Report on Intrusion Detection Systems, prepared by Victor H. Marshall, Systems Assurance Team Leader, Booz, Allen & Hamilton Inc. This document can be found online at

In any event, this "live" testing technique should be primarily employed where there is a single attack point. Typical situations are where you suspect that one of the workstations is the most viable target (where perhaps the others will refuse all connections from outside the subnet and so forth). Obviously, I am not suggesting that you erect an exact model of the target network; that could be cost and time prohibitive. What I am suggesting is that in coordination of a remote attack, you need to have (at a minimum) some idea of what is supposed to happen. Simulating that attack on a host other than the target is a wise thing to do. Otherwise, there is no guarantee that you can even marginally ensure that the data you receive back has some integrity. Bellovin's paper on Berferd should be a warning to any cracker that a simulation of a vulnerable network is not out of the question. In fact, I have wondered many times why security technologies have not focused entirely on this type of technique, especially since scanners have become so popular.

What is the difficulty in a system administrator creating his own such system on the fly? How difficult would it be for an administrator to write custom daemons (on a system where the targeted services aren't even actually running) that would provide the cracker with bogus responses? Isn't this better than announcing that you have a firewall (or TCP_WRAPPER), therefore alerting the attacker to potential problems? Never mind passive port-scanning utilities, let's get down to the nitty-gritty: This is how to catch a cracker--with a system designed exclusively for the purpose of creating logs that demonstrate intent. This, in my opinion, is where some new advances ought to be made. These types of systems offer automation to the process of evidence gathering.

The agencies that typically utilize such tools are few. Mostly, they are military organizations. An interesting document is available on the Internet in regard to military evaluations and intrusion detection. What is truly interesting about the document is the flair with which it is written. For instance, sample this little excerpt:

For 20 days in early spring 1994, Air Force cybersleuths stalked a digital delinquent raiding unclassified computer systems at Griffiss AFB, NY. The investigators had staked out the crime scene--a small, 12-by-12-foot computer room in Rome Laboratory's Air Development Center--for weeks, surviving on Jolt cola, junk food and naps underneath desks. Traps were set by the Air Force Information Warfare Center to catch the bandit in the act, and `silent' alarms sounded each time their man slinked back to survey his handiwork. The suspect, who dubbed himself `Data Stream,' was blind to the surveillance, but despite this, led pursuers on several high-speed chases that don't get much faster--the speed of light. The outlaw was a computer hacker zipping along the ethereal lanes of the Internet, and tailing him was the information superhighway patrol--the Air Force Office of Special Investigations computer crime investigations unit.

Cross Reference: The previous paragraph is excerpted from "Hacker Trackers: OSI Computer Cops Fight Crime On-Line" by Pat McKenna. It can be found online at

The document doesn't give as much technical information as one would want, but it is quite interesting, all the same. Probably a more practical document for the legal preservation of information in the investigation of intrusions is one titled "Investigating and Prosecuting Network Intrusions." It was authored by John C. Smith, Senior Investigator in the Computer Crime Unit of the Santa Clara County District Attorney's Office.

Cross Reference: "Investigating and Prosecuting Network Intrusions" can be found online at

In any event, as I have said, at least some testing should be done beforehand. That can only be done by establishing a like box with like software.

Tools: About Holes and Other Important Features

Next, you need to assemble the tools you will actually use. These tools will most probably be scanners. You will be looking (at a minimum) to identify all services now running on the target. Based on your analysis of the operating system (as well as the other variables I've mentioned in this chapter), you will need to evaluate your tools to determine what areas or holes they do not cover.

In instances where a particular service is covered by one tool but not another, it is best to integrate the two tools together. The ease of integration of such tools will depend largely on whether these tools can simply be attached as external modules to a scanner like SATAN or SAFESuite. Again, here the use of a test run can be extremely valuable; in most instances, you cannot simply attach an external program and have it work flawlessly.

To determine the exact outcome of how all these tools will work in concert, it is best to do this at least on some machine (even if it is not identical to the target). That is because, here, we are concerned with whether the scan will be somehow interrupted or corrupted as the result of running two or more modules of disparate design. Remember that a real-time scanning attack should be done only once. If you screw it up, you might not get a second chance.

So, you will be picking your tools (at least for the scan) based on what you can reasonably expect to find at the other end. In some cases, this is an easy job. For example, perhaps you already know that someone on the box is running X Window System applications across the Net. (Not bloody likely, but not unheard of.) In that case, you will also be scanning for xhost problems, and so it goes.

Remember that a scanner is a drastic solution. It is the equivalent of running up to an occupied home with a crowbar in broad daylight, trying all the doors and windows. If the system administrator is even moderately tuned into security issues, you have just announced your entire plan.

TIP: There are some measures you can take to avoid that announcement, but they are drastic: You can actually institute the same security procedures that other networks do, including installing software (sometimes a firewall and sometimes not) that will refuse to report your machine's particulars to the target. There are serious problems with this type of technique, however, as they require a high level of skill. (Also, many tools will be rendered useless by instituting such techniques. Some tools are designed so that one or more functions require the ability to go out of your network, through the router, and back inside again.)

Again, however, we are assuming here that the target is not armored; it's just an average site, which means that we needn't stress too much about the scan. Furthermore, as Dan Farmer's recent survey suggests, scanning may not be a significant issue anyway. According to Farmer (and I have implicit faith in his representations, knowing from personal experience that he is a man of honor), the majority of networks don't even notice the traffic: attempt was made to hide the survey, but only three sites out of more than two thousand contacted me to inquire what was going on when I performed the unauthorized survey (that's a bit over one in one thousand questioning my activity). Two were from the normal survey list, and one was from my random group.

Cross Reference: The preceding paragraph is excerpted from the introduction of Shall We Dust Moscow? by Dan Farmer. This document can be found online at

That scan involved over 2,000 hosts, the majority of which were fairly sensitive sites (for example, banks). You would expect that these sites would be ultra-paranoid, filtering every packet and immediately jumping on even the slightest hint of a scan.

Developing an Attack Strategy

The days of roaming around the Internet, cracking this and that server are basically over. Years ago, compromising the security of a system was viewed as a minor transgression as long as no damage was done. Today, the situation is different. Today, the value of data is becoming an increasingly talked-about issue. Therefore, the modern cracker would be wise not to crack without a reason. Similarly, he would be wise to set forth cracking a server only with a particular plan.

The only instance in which this does not apply is where the cracker is either located in a foreign state that has no specific law against computer intrusion (Berferd again) or one that provides no extradition procedure for that particular offense (for example, the NASA case involving a student in Argentina). All other crackers would be wise to tread very cautiously.

Your attack strategy may depend on what you are wanting to accomplish. We will assume, however, that the task at hand is basically nothing more than compromise of system security. If this is your plan, you need to lay out how the attack will be accomplished. The longer the scan takes (and the more machines that are included within it), the more likely it is that it will be immediately discovered. Also, the more scan data that you have to sift through, the longer it will take to implement an attack based upon that data. The time that elapses between the scan and the actual attack, as I've mentioned, should be short.

Some things are therefore obvious (or should be). If you determine from all of your data collection that certain portions of the network are segmented by routers, switches, bridges, or other devices, you should probably exclude those from your scan. After all, compromising those systems will likely produce little benefit. Suppose you gained root on one such box in a segment. How far do you think you could get? Do you think that you could easily cross a bridge, router, or switch? Probably not. Therefore, sniffing will only render relevant information about the other machines in the segment, and spoofing will likewise work (reliably) only against those machines within the segment. Because what you are looking for is root on the main box (or at least, within the largest network segment available), it is unlikely that a scan on smaller, more secure segments would prove to be of great benefit.

NOTE: Of course, if these machines (for whatever reason) happen to be the only ones exposed, by all means, attack them (unless they are completely worthless). For example, it is a common procedure to place a Web server outside the network firewall or make that machine the only one accessible from the void. Unless the purpose of the exercise is to crack the Web server (and cause some limited, public embarrassment to the owners of the Web box), why bother? These machines are typically "sacrificial" hosts--that is, the system administrator has anticipated losing the entire machine to a remote attack, so the machine has nothing of import upon its drives. Nothing except Web pages, that is.

In any event, once you have determined the parameters of your scan, implement it.

A Word About Timing Scans

When should you implement a scan? The answer to this is really "never." However, if you are going to do it, I would do it late at night relative to the target. Because it is going to create a run of connection requests anyway (and because it would take much longer if implemented during high-traffic periods), I think you might as well take advantage of the graveyard shift. The shorter the time period, the better off you are.

After the Scan

After you have completed the scan, you will be subjecting the data to analysis. The first issue you want to get out of the way is whether the information is even authentic. (This, to some degree, is established from your sample scans on a like machine with the like operating system distribution.)

Analysis is the next step. This will vary depending upon what you have found. Certainly, the documents included in the SATAN distribution can help tremendously in this regard. Those documents (tutorials about vulnerabilities) are brief, but direct and informative. They address the following vulnerabilities:

  • FTP vulnerabilities
  • NFS export to unprivileged programs
  • NFS export via portmapper
  • NIS password file access
  • REXD access
  • SATAN password disclosure
  • Sendmail vulnerabilities
  • TFTP file access
  • Remote shell access
  • Unrestricted NFS export
  • Unrestricted X server access
  • Unrestricted modem
  • Writeable FTP home directory

In addition to these pieces of information, you should apply any knowledge that you have gained through the process of gathering information on the specific platform and operating system. In other words, if a scanner reports a certain vulnerability (especially a newer one), you should refer back to the database of information that you have already built from raking BUGTRAQ and other searchable sources.

This is a major point: There is no way to become either a master system administrator or a master cracker overnight. The hard truth is this: You may spend weeks studying source code, vulnerabilities, a particular operating system, or other information before you truly understand the nature of an attack and what can be culled from it. Those are the breaks. There is no substitute for experience, nor is there a substitute for perseverance or patience. If you lack any of these attributes, forget it.

That is an important point to be made here. Whether we are talking about individuals like Kevin Mitnik (cracker) or people like Weitse Venema (hacker), it makes little difference. Their work and their accomplishments have been discussed in various news magazines and online forums. They are celebrities within the Internet security (and in some cases, beyond). However, their accomplishments (good or bad) resulted from hard work, study, ingenuity, thought, imagination, and self-application. Thus, no firewall will save a security administrator who isn't on top of it, nor will SATAN help a newbie cracker to unlawfully breach the security of a remote target. That's the bottom line.


Remote attacks are becoming increasingly common. As discussed in several earlier chapters, the ability to run a scan has become more within the grasp of the average user. Similarly, the proliferation of searchable vulnerability indexes have greatly enhanced one's ability to identify possible security issues.

Some individuals suggest that the free sharing of such information is itself contributing to the poor state of security on the Internet. That is incorrect. Rather, system administrators must make use of such publicly available information. They should, technically, perform the procedures described here on their own networks. It is not so much a matter of cost as it is time.

One interesting phenomenon is the increase in tools to attack Windows NT boxes. Not just scanning tools, either, but sniffers, password grabbers, and password crackers. In reference to remote attack tools, though, the best tool available for NT is SAFEsuite by Internet Security Systems (ISS). It contains a wide variety of tools, although the majority were designed for internal security analysis.

For example, consider the Intranet Scanner, which assesses the internal security of a network tied to a Microsoft Windows NT server. Note here that I write only that the network is tied to the NT server. This does not mean that all machines on the network must run NT in order for the Intranet Scanner to work. Rather, it is designed to assess a network that contains nodes of disparate architecture and operating systems. So, you could have boxes running Windows 95, UNIX, or potentially other operating systems running TCP/IP. The title of the document is "Security Assessment in the Windows NT Environment: A White Paper for Network Security Professionals." It discusses the many features of the product line and a bit about Windows NT security in general.

Cross Reference: To get a better idea of what Intranet Scanner offers, check out

Specific ways to target specific operating systems (as in "How To" sections) are beyond the scope of this book, not because I lack the knowledge but because it could take volumes to relate. To give you a frame of reference, consider this: The Australian CERT (AUSCERT) UNIX Security Checklist consists of at least six pages of printed information. The information is extremely abbreviated and is difficult to interpret by anyone who is not well versed in UNIX. Taking each point that AUSCERT raises and expanding it into a detailed description and tutorial would likely create a 400-page book, even if the format contained simple headings such as Daemon, Holes, Source, Impact, Platform, Examples, Fix, and so on. (That document, by the way, discussed elsewhere in this book, is the definitive list of UNIX security vulnerabilities. It is described in detail in Chapter 17, "UNIX: The Big Kahuna.")

In closing, a well-orchestrated and formidable remote attack is not the work of some half-cocked cracker. It is the work of someone with a deep understanding of the system--someone who is cool, collected, and quite well educated in TCP/IP. (Although that education may not have come in a formal fashion.) For this reason, it is a shame that crackers usually come to such a terrible end. One wonders why these talented folks turn to the dark side.

I know this, though: It has nothing to do with money. There are money-oriented crackers, and they are professionals. But the hobbyist cracker is a social curiosity--so much talent and so little common sense. It is extraordinary, really, for one incredible reason: It was crackers who spawned most of the tools in this book. Their activities gave rise to the more conventional (and more talented) computing communities that are coding special security applications. Therefore, the existence of specialized tools is really a monument to the cracking community. They have had a significant impact, and one such impact was the development of the remote attack. The technique not only exists because of these curious people, but also grows in complexity because of them.

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