|
26.2 Can You Trust Your Suppliers?Your computer does something suspicious. You discover that the modification dates on your system software have changed. It appears that an attacker has broken in, or that some kind of virus is spreading. So what do you do? You save your files to backup tapes, format your hard disks, and reinstall your computer's operating system and programs from the original distribution media. Is this really the right plan? You can never know. Perhaps your problems were the result of a break-in. But sometimes, the worst is brought to you by the people who sold you your hardware and software in the first place. 26.2.1 Hardware BugsIn 1994, the public learned that Intel Pentium processors had a floating-point problem that infrequently resulted in a significant loss of precision when performing some division operations. Not only had Intel officials known about this, but apparently they had decided not to tell their customers until after there was significant negative public reaction. Several vendors of disk drives have had problems with their products failing suddenly and catastrophically, sometimes within days of being initially used. Other disk drives failed when they were used with Unix, but not with the vendor's own proprietary operating system. The reason: Unix did not run the necessary command to map out bad blocks on the media. Yet these drives were widely bought for use with the Unix operating system. Furthermore, there are many cases of effective self-destruct sequences in various kinds of terminals and computers. For example, Digital's original VT100 terminal had an escape sequence that switched the terminal from a 60 Hz refresh rate to a 50 Hz refresh rate, and another escape sequence that switched it back. By repeatedly sending the two escape sequences to a VT100 terminal, a malicious programmer could cause the terminal's flyback transformer to burn out—sometimes spectacularly! A similar sequence of instructions could be used to break the monochrome monitor on the original IBM PC video display. 26.2.2 Viruses on the Distribution DiskA few years ago, there was a presumption in the field of computer security that manufacturers who distributed computer software took the time and due diligence to ensure that their computer programs, if they were not free of bugs and defects, were at least free of computer viruses and glaring computer security holes. Users were warned not to run shareware and not to download programs from bulletin board systems because such programs were likely to contain viruses or Trojan horses. Indeed, at least one company that manufactured a shareware virus-scanning program made a small fortune telling the world that everybody else's shareware programs were potentially unsafe. Time and experience have taught us otherwise. In recent years, a few viruses have been distributed with shareware, but we have also seen many viruses distributed in shrink-wrapped programs. The viruses come from small companies, and from the makers of major computer systems. Several times in the last decade Microsoft has distributed CD-ROMs with viruses on them, including one with the first in-the-wild macro virus (the "Concept" virus for Microsoft Word). The Bureau of the Census has distributed a CD-ROM with a virus on it. One of the problems posed by viruses on distribution disks is that many installation procedures require that the user disable any antiviral software that is running. In the last few years, email has become a major vector for macro viruses. Several security companies that have standardized on Microsoft products have unwittingly distributed viruses to their customers, clients, and the press. In almost all cases, these viruses have been distributed because the companies had an insufficiently patched version of Outlook.[4]
The mass-market software industry also has problems with logic bombs and Trojan horses. For example, in 1994, Adobe distributed a version of a new Photoshop 3.0 for the Macintosh with a "time bomb" designed to make the program stop working at some point; the time bomb had inadvertently been left in the program from the beta-testing cycle. In 2001 a popular form-filling program named Gator started displaying its own advertisements on top of other banner advertisements on web pages. Later, the program started popping up windows with advertisements on the user's desktop when the user was running other programs. In 2002, we are seeing products, including Microsoft's media player, shipped with end user license agreements suggesting that they may automatically download and install digital rights management and surveillance code without user knowledge. Because commercial software is not distributed in source code form, you cannot inspect a program and tell if these kinds of intentional "bugs" are present or not. As with shrink-wrapped programs, shareware is also a mixed bag. Some shareware sites have system administrators who are very conscientious and go to great pains to scan their software libraries with viral scanners before making them available for download. Other sites have no controls, and allow users to place files directly in the download libraries. In the spring of 1995, a program entitled PKZIP30.EXE made its way around a variety of FTP sites on the Internet and through America Online. This program appeared to be the 3.0 beta release of PKZIP, a popular DOS compression utility. But when the program was run, it erased the user's hard disk. This kind of attack seems to recur every 3-4 years. 26.2.3 Buggy SoftwareConsider the following, rather typical, disclaimer on a piece of distributed software:
Software always has bugs. You install it on your disk, and under certain circumstances, it damages your files or returns incorrect results. The examples are legion. You may think that the software is infected with a virus—it is certainly behaving as if it is infected with a virus—but the problem is merely the result of poor programming. If the creators and vendors of the software don't have confidence in their own software, why should you? If the vendors disclaim " . . . warranty as to [its] performance, merchantability, or fitness for any particular purpose," then why are you paying them money and using their software as a base for your business? For too many software vendors, quality is not a priority. In most cases, they license the software to you with a broad disclaimer of warranty (similar to the one above) so there is little incentive for them to be sure that every bug has been eradicated before they go to market. The attitude is often one of "We'll fix it in the next release, after the customers have found all the major bugs." Then they introduce new features with new flaws. Yet people wait in line at midnight to be the first to buy software that is full of errors and may erase their disks when they try to install it. (Vendors counter by saying that users are not willing to pay for quality, and that users value time-to-market far more than they do quality or security.) Other problems abound. Recall that the first study by Professor Barton Miller (cited in Chapter 16) found that more than one-third of common programs supplied by several Unix vendors crashed or hung when they were tested with a trivial program that generated random input. Five years later, he reran the tests. The results? Although most vendors had improved to where "only" one-fourth of the programs crashed, one vendor's software exhibited a 46% failure rate! This failure rate occurred despite wide circulation and publication of the report, and despite the fact that Miller's team made the test code available to vendors for free. Although we don't know the results of the same tests that have been run recently, anecdotal experience indicates that similarly dismal results should be expected from many of today's vendors. Most frightening, the testing performed by Miller's group is one of the simplest, least effective forms of testing that can be performed (random, black-box testing). Do vendors do any reasonable testing at all? Consider the case of a software engineer from a major PC software vendor who came to Purdue to recruit in 1995. During his presentation, students reported that he stated that 2 of the top 10 reasons to work for his company were "You don't need to bother with that software engineering stuff—you simply need to love to code" and "You'd rather write assembly code than test software." As you might expect, the company has developed a reputation for very bad software quality problems. What is somewhat surprising is that they continue to be a market leader, year after year, and that people continue to buy their software.[5]
What are your vendor's policies about testing and good software-engineering practices? Or consider the case of someone who implements security features without really understanding the "big picture." As we noted in Section 16.7.2 in Chapter 16, a sophisticated encryption algorithm was built into Netscape Navigator to protect credit card numbers in transit on the network. Unfortunately, the implementation used a weak initialization of the "random number" used to generate a system key. The result? Someone with an account on a client machine could easily obtain enough information to crack the key in a matter of seconds, using only a small program. 26.2.4 Hacker ChallengesOver the past dozen years, several vendors have issued public announcements stating that their systems are secure because they haven't been broken during "hacker challenges." Usually, these challenges involve some vendor putting its system on the Internet and inviting all comers to take a whack in return for some token prize. Then, after a few weeks or months, the vendor shuts down the site, proclaims their product invulnerable, and advertises the results as if they were a badge of honor. But consider the following:
Furthermore, the whole process sends the wrong message—that we should build things and then try to break them (rather than building them right in the first place), or that there is some prestige or glory in breaking systems. We don't test the strengths of bridges by driving over them with a variety of cars and trucks to see if they fail, and pronounce them safe if no collapse occurs during the test. Some software designers could learn a lot from civil engineers. So might the rest of us. In ancient times, if a house fell or a bridge collapsed and injured someone, the engineer who designed it was crushed to death in the rubble as punishment! Roman engineers were required to stand under their bridges when they were used the first few times. Some of those bridges are still standing—and in use—2,000 years later. Next time you see an advertiser using a challenge to sell a product, you should ask if the challenge is really giving you more confidence in the producct . . . or convincing you that the vendor doesn't have a clue as to how to really design and test security. If you think that a security challenge builds the right kind of trust, then get in touch with us. We have these magic pendants. No one wearing one has ever had a system broken into, despite challenges to all the computer users who happened to be around when the systems were developed. Thus, the pendants must be effective at keeping out attackers. We'll be happy to sell some to you. After all, we employ the same rigorous testing methodology as your security software vendors, so our product must be reliable, right? 26.2.5 Security Bugs That Never Get FixedThere is also the question of legitimate software distributed by computer manufacturers that contains glaring security holes. More than a year after the release of sendmail Version 8, nearly every major Unix vendor was still distributing its computers equipped with sendmail Version 5. (Versions 6 and 7 were interim releases that were never released.) While Version 8 had many improvements over Version 5, it also had many critical security patches. Was the unwillingness of Unix vendors to adopt Version 8 negligence—a demonstration of their laissez-faire attitude towards computer security—or merely a reflection of pressing market conditions?[6] Are the two really different?
How about the case in which many vendors released versions of TFTP that, by default, allowed remote users to obtain copies of the password file? What about versions of RPC that allow users to spoof NFS by using proxy calls through the RPC system? What about software that includes a writable utmp file that enables a user to overwrite arbitrary system files? Each of these cases is a well-known security flaw. In each case, the vendors did not provide fixes for years—even now, they may not be fixed everywhere, more than a decade after some of these were first identified as problems. Many vendors say that computer security is not a high priority because they are not convinced that spending more money on computer security will pay off for them. Computer companies are rightly concerned with the amount of money that they spend on computer security. Developing a more secure computer is an expensive proposition that not every customer may be willing to pay for. The same level of computer security may not be necessary for a server on the Internet as for a server behind a corporate firewall, or on a disconnected network. Furthermore, increased computer security will not automatically increase sales. Firms that want security generally hire staff who are responsible for keeping systems secure; users who do not want (or do not understand) security are usually unwilling to pay for it at any price, and frequently disable security when it is provided. On the other hand, a computer company is far better equipped to safeguard the security of its operating system than an individual user is. One reason is that a computer company has access to the system's source code. A second reason is that most large companies can easily devote two or three people to assuring the security of their operating system, whereas most businesses are hard-pressed to devote even a single full-time employee to the job of computer security. This can be a place where open source software shines. By providing the source code freely to hundreds or thousands of users (or more), any security flaws present may be found more quickly in open source operating systems and applications, and are more likely to be disclosed and fixed. The patch that fixes the flaw is itself open to review by the users, which tends to ensure that few security patches are released that cause more damage than they prevent. We believe that more and more computer users are beginning to see system security and software quality as distinguishing features, much in the way that they see usability, performance, and new functionality as features. When a person breaks into a computer, over the Internet or otherwise, the act reflects poorly on the maker of the software. We hope that more computer companies will make software quality at least as important as new features. Vendors that rush fault-ridden code to the market should be penalized by their customers, not rewarded for giving customers access to "beta software." 26.2.6 Network Providers That Network Too WellNetwork providers pose special challenges for businesses and individuals. By their nature, network providers have computers that connect directly to your computer network, placing the provider (or perhaps a rogue employee at the providing company) in an ideal position to launch an attack against your installation. Also, providers are usually in possession of confidential billing information belonging to the users. Some providers even have the ability to directly make charges to a user's credit card or deduct funds from a user's bank account. Dan Geer, a well-known computer security professional, tells an interesting story about an investment brokerage firm that set up a series of direct IP connections between its clients' computers and the computers at the brokerage firm. The purpose of the links was to allow the clients to trade directly on the brokerage firm's computer system. But as the client firms were also competitors, the brokerage house equipped the link with a variety of sophisticated firewall systems. It turns out, says Geer, that although the firm had protected itself from its clients, it did not invest the time or money to protect the clients from each other. One of the firm's clients used the direct connection to break into the system operated by another client. A significant amount of proprietary information was stolen before the intrusion was discovered. In another case, a series of articles appearing in The New York Times during the first few months of 1995 revealed how hacker Kevin Mitnick allegedly broke into a computer system operated by Netcom Communications. One of the things that Mitnick is alleged to have stolen was a complete copy of Netcom's client database, including the credit card numbers for more than 30,000 of Netcom's customers. Certainly, Netcom needed the credit card numbers to bill its customers for service. But why were they placed on a computer system that could be reached from the Internet? Why were they not encrypted? Five years later, history repeated itself on a much larger scale, as web sites belonging to numerous companies, including EggHead Software and CD Universe, were broken into, and hundreds of thousands of credit card numbers were covertly downloaded. Think about all those services on the Web. They claim to use all kinds of super encryption protocols to safeguard your credit card number as it is sent across the network. But remember—you can reach their machines via the Internet to make the transaction. What kinds of safeguards do they have in place at their sites to protect all the card numbers after they're collected? Simply encrypting the connection is not sufficient. As Spafford originally said in a conference address in 1995:
|
|
|