Book Review: Web Hacking: Attacks and Defense LG #91

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...making Linux just a little more fun! | Book Review: Web Hacking: Attacks and Defense By John B Cole

The guys at Addison-Wesley are cool in that they give my LUG free books, and judging by the titles we have received lately, web site security is something readers cannot get enough of. I am not going to bother regurgitating the meaningless blurbs on the back cover, nor the lengthy credentials of the authors; instead, I am going to focus on a simple question: can this book teach a working web developer useful lessons? If it does, it is worth the $49.99 cover price and if it does not I can use it in my fireplace. I am quite critical of expensive books which grossly overreach and as a result are unsatisfying to all readers. Let us see how "Web Hacking" stacks up...

"Web Hacking" is divided into four major sections: The E-Commerce? Playground, URLs Unraveled, How Do They Do It?, and Advanced Web Kung Fu. The authors are off to a good start - they (unlike about 99% of the posters on Slashdot) realize that "URLs" does not require an apostrophe. That is enough for a whole star even if the rest of the book is copied, grammatical errors and all, from Usenet archives (although the Gentle Reader should note that I am making no such assertion). The authors utilize a chatty, conversational style of prose over an academic style, which is appropriate for this book.

"The E-Commerce? Playground" leads off with a simple case study demonstrating an effective attack on a small business web site using only HTTP. The attacker exploited a poorly-written Perl script in the attack, and I hope we all realize that there is far more badly-written Perl in the world than not (the Reviewer must grudgingly admit that he has on occasion, contributed to that very problem). The authors point out that firewalls and intrusion detection systems are largely useless, and they will continue to emphasize this throughout the book. All of us would do well to remember that lesson. Sure, the attack in the case study would not work against Amazon or Dell, but there are a lot of small web sites that are ripe for the plucking...and one of those sites may have your credit card number. Chapter 1, Web Languages, covers everything from Perl to ASP in a nutshell. The idea here is more to demonstrate that every language (even HTML) has vulnerabilities that can be exploited by a knowledgeable hacker. Most web developers and system administrator will not learn anything new here, but pray that your boss does not skip this chapter before he picks the Perfect Language for your company's Web Site of Tomorrow. Chapter 2, Web and Database Servers, is very brief and only discusses Apache and IIS on the web server front and MS SQL Server and Oracle on the database front. I suppose it is not big deal that other web servers are not discussed, but it is worth noting that there are many different HTTP servers, and they turn up in the oddest places (What's running on your production servers? Are you sure?) A security-themed chapter written for enterprise-level customers, the sort who actually own licenses for Oracle and MS SQL Server, would be better off as a book. I am disappointed to see no discussion of MySQL or PostgreSQL here. More sites than you can shake a stick at, particularly mom-and-pop type businesses, are running MySQL on the backend, and there are a lot of poorly-secured MySQL installations in the world (-1/2 star). Chapter 3, Shopping carts and Payment Gateways, was largely new material for me. I was familiar with older attacks on systems which used client-side cookies and GET variables to store important (e.g. price) information. I had not considered some the attacks involving payment validation systems, and the examples in the book underscore the consequences of sloppy design. Chapter 4, HTTP and HTTPS: The Hacking Protocols, is included in large part to emphasize the fact that all an attacker needs is a URL to make you regret your choice of careers. That aside, its coverage of the HTTP and HTTPS protocols is useful as a thumbnail review, but the chapter will be of dubious value to a network novice. Chapter 5, URL: The Web Hacker's Sword, ends Section 1. This chapter is prefaced with a quote from "Star Wars Episode IV: A New Hope", which demonstrates clearly the geek-worthiness of the authors. Chapter 5 actually covers URL hacks, such as URL structure and encoding, as well as meta-character mischief and HTML forms. Some of the attacks described will only work with GET variables, which are visible to the user through the URL. So, a simple tip for avoiding easy web hacks might be: use sessions for persistent data and pass data from the browser to the server in POST variables. You have been warned. The material on metacharacters and form processing focus on the issue of user input processing. I have worked at universities for a long time, and believe when I tell you that you should never trust user input. Ever. As a whole, Section 1 of "Web Hacking" is useful to novice administrators and developers or managers; experienced professionals are unlikely to find anything new here.

Section 2, "URLs Unraveled", leads off with another case study. This case study demonstrates how a savvy hacker might analyze a web site based on the URLs exposed to the public, and use that knowledge to launch an attack. This case study serves to motivate the rest of the section. Chapter 6, Web: Under (the) Cover, provides an overview of web application structure, as well as the methods used by hackers to dissect target systems. There is all odd manner of thing in here, including web server APIs, ODBC, and JDBC. There is even a handy chart to help you match extensions to server platforms. The authors even mention some things you can do to limit your exposure, and one of the better ideas (IMHO) is to prevent the leakage of error and messages to the browser. Skim this chapter and look at the examples. Chapter 7, Reading Between the Lines, focuses on methods of analyzing HTML source (via "View Page Source") to identify vulnerabilities and develop attacks. Cool stuff here that can easily be overlooked during short, rapid development cycles. There is even an example of some nefarious uses of wget and grep. Chapter 8, Site Linkage Analysis, continues the exploration of site analytic methods. This chapter focuses principally on the uses of several software tools for site analysis, all of which are Windows tools (except for wget). I am torn about this section. Much of the material seems quite obvious, but that is because I was already familiar with it. However, I feel that all novices and many seasoned professionals can learn from the material in this section. No deduction.

Section 3, "How Do They Do It", purports to be the real heart of the book, the "Great Magic Tricks Revealed" of the web hacking world. Chapter 9, Cyber Graffiti, covers the web site defacement attacks typically reported in the media. A detailed case study covers a number of security issues, including proxy server configuration, HTTP authentication, and directory browsing. Good stuff. Chapter 10, E-Shoplifting?, provides a case study of an e-commerce system pieced together from several vendors (get this - an Access backend...). The basic attack was based on client-side forms validation and the use of hidden fields to pass price information. A site overhaul to address the risks exposed by an audit is detailed. Chapter 11, Database Access, is short but mentions some interesting attacks, as well as sound countermeasures. Chapter 13, Java: Remote Command Execution, was new ground for me. I would generally rather have hot pokers stuck in my eyes or program in COBOL than even look at Java source. However, being a savvy developer, I am well aware of the popularity of Java. I learned some neat stuff in this chapter, but the key take-home message is that you should always sanitize and screen user input. Countermeasures based on servlet management are also discussed. Chapter 13, Impersonation, deals with sessions, session hijacking, and cookies. This chapter is sort of interesting, but unless a developer does something spectacularly foolish, such as using a system which generates guessable session IDs or stores important data on the client using cookies, these attacks are not a prominent threat. Of greater concern might be physical security to prevent copies of cookies on a user's machine from being stolen. Chapter 14, Buffer Overflows: On-the-Fly?, could be a book in its own right. Almost every vulnerability I hear about these days is due to a buffer overflow. This chapter covers pretty technical material, and the reckless reader might be faced with some C or ASM code fragments; if your hair is pointy, you have been warned. I am not sure that this chapter is very valuable other than to highlight the fact that not every web site vulnerability is due to poor programming or systems administration on the part of the consumer of information systems. Sun, IBM, Microsoft, and their ilk have all shipped numerous products with buffer overflows that have been identified. Even vendors make mistakes. Section 3 is what we all opened the book to read. On the whole, it is worthwhile reading. The authors do a very good job of dissecting attacks, and of emphasizing simple countermeasures such as "validate all input, whatever the source".

Section 4, "Advanced Web Kung Fu", perked my ears up. Is this Keanu Reeves "Whoa, I know kung fu!"-type insight, or more pedestrian "Oh yeah, I heard about that somewhere"-type insight? Chapter 15, "Web Hacking: Automated Tools" is simply an overview of some commonly-used hacking tools. Frankly, I have only heard of netcat because it was the only Unix tool discussed. I'm never going to beat an agent at this rate... Chapter 16, "Worms", is just an overview of a few famous worms that have ravaged the Internet like Germany pillaging France. I'm never going to be on "Kung Fu Theater"! Chapter 17, "Beating the IDS", covers some interesting things that you can do to intrusion detection systems (IDS), but is simply a curiosity. This section is more like "hitting a drunk guy with a pool cue when he isn't looking" than "advanced kung fu", and is the most disappointing part of the book. It feels like three chapters of briefs written for PHBs so that they can feel savvy at the end of the day. Shame on you guys, you were doing so well (-1 star).

There is little excuse for any competent developer today to deploy an application susceptible to most of the attacks detailed in this book (the use of sessions alone would foil many of these attacks), but the book is a worthwhile read for novice developers and managers in general. More experienced developers should read it at the bookstore while on a coffee break or yoink it from the intern. Is the book worth $49.99? I am afraid that I must say "No". $24.99 is a much more reasonable price, the thickness (492pp.) of "Web Hacking" notwithstanding (-1/2 star).

John is a scientist and programmer who has been using Linux since 1998, when a deranged - and somewhat frightening - colleague insisted that there was A Better Way. John is a supporter of free software, and has written several applications to support his research, and scratch itches, in PHP and Python. On several memorable occasions, he wrote PHP program that called Python programs, parsed the output streams, and presented the results. He promises to not do that anymore.

John is currently using Mandrake 9.1 on his desktop machine, but is going to switch to Gentoo and prove his manliness any day now.

John will be happy to tell you about his research in animal breeding and quantitative genetics just as soon as he can find a scrap of paper. You see, this next bit is rather technical...

Copyright © 2003, John B Cole. Copying license http://www.linuxgazette.com/copying.html
Published in Issue 91 of Linux Gazette, June 2003

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