Exploiting Software

prostoalex writes "Why are networked computing environments so insecure? You've heard the story before - early computers were not designed to work in the network environment, and even most software written later was designed to work on benevolent networks. As Bruce Schneier says in the preface to Building Secure Software: How to Break Code, 'We wouldn't have to spend so much time, money and effort on network security if we didn't have such bad software security.'" Read on for prostoalex's review of Exploiting Software, which aims to balance that situation somewhat. Exploiting Software: How to Break Code author Greg Hoglund, Gary McGraw pages 512 publisher Addison Wesley Professional rating 8 reviewer Alex Moskalyuk ISBN 0201786958 summary Techniques and software used to attack applications.

What kind of secure are you after? There are many published titles on the topic of software security are numerous, but most of them follow certain patterns. Building Secure Software by Viega and McGraw was mainly concerned with proper techniques and general software engineering mindset without going into specifics. Then there was Writing Secure Code , by Howard and LeBlanc, which provided concrete examples and showed the "right way" to do secure coding. I heard the title instantly became a required reading at world's largest software corporation. It's currently in its second edition.

Secure Programming Cookbook for C/C++ by Viega and Messier, was the hands-on title for those developing C/C++ application with security in mind, as the cookbook recipes generally gave examples of good code, with each chapter providing some general background information on the topic discussed (I reviewed it on Slashdot in September last year).

Just in case you were wondering, the list above wasn't just retrieved by a quick search at Amazon. My Master's degree, completed last summer, dealt with the topic of software security, and those are the titles I've read preparing to write the theoretical part.

From the other side With the variety of books on how to write secure software, and what techniques to use to make existing software more secure, there was a niche for a book targeted specifically to those who wanted to break software. Black hat or white hat, the network security experts always had titles like Hacking Exposed to give them an idea of what was available in terms of techniques and methodologies used out there. For software security most of the articles and books generally would tell you something in the terms "do not use strcpy(), as it introduces buffer overruns".

Great, so I won't use strcpy(), did it make my application more secure? Is it more or less hack-proof? What if I am a tester and required to play with this aspect of the application to ensure the application's security before the product ships? Theoretically hanging out at proper IRC rooms and getting lifetime Phrack and 2600 subscriptions should be enough to cover you at the beginning, however, the learning curve here leaves much to be desired, let alone the fact you will probably be kicked out of the IRC rooms for asking n00b questions. Another path would be to take an expensive training course by someone with a name in the industry, but the price tag for those generally leaves out self-learners and those operating on limited budgets, which adds up to about 99% of software engineers and testers out there.

Exploiting Software to the rescue.

Exploiting Software fills the void that existed in this market. Eight chapters take you through the basics and some advanced techniques of attacking software applications with the purpose of executing arbitrary code supplied by an attacker (you).

The book mainly deals with Windows applications for x86 platforms, and some knowledge of C/C++ and Win32 API is required to go through the example applications. To automate some processes and demonstrate possible attacks the authors use Perl, so knowledge of that would help the reader, too. Some chapters, (e.g. the buffer overflow one) show disassembler output, and while you're not expected to read x86 ASM code as if it were English, knowledge of how the registers work and how the subprocedure calls are handled on this Intel architecture are required. After all, if potential attackers know it, you better familiarize yourself with some low-level code, too.

While discussing various possible attacks, the authors post different attack patterns. The patterns themselves usually appear in gray textboxes and talk about the possible exploit in general terms. After that, a series of attack examples follow, with specific descriptions on what can be done, and how. For example, the attack pattern on page 165 is titled "Leverage executable code in non-executable files." The following attack example is "Executable fonts," and it talks how the font files are generally treated by the Windows systems (they are a special form of DLLs). Thus it's possible to embed some executable code into a font library you're creating, for which the authors provide an example in Microsoft Visual Studio.

What's cool is that all the attack patterns are listed in a separate table of contents (alas, not on the Web site table of contents, which just lists the chapters and subchapters), so you can browse to the attack pattern you decide to learn about, read some general info about it and then study specific examples. The examples themselves are not in the table of contents, which I think is a mistake, as it would make searching for possible patterns much easier. After all, how are you supposed to know that "Informix database file system" (p. 189) is under "Relative path traversal" pattern? Well, unless you know specifically that the line http://[Informix database host]/ifx/?LO=../../../etc/ is the one discussed in the example, you would have to either go through the index hoping no omissions were made, or read the chapter in its entirety.

One of the best chapters of the book, Reverse Engineering and Program Understanding, which provides a good introduction into techniques used throughout the book, is available online from Addison Wesley. By having a free chapter you already have 1/8th of the book, but don't think that the low number of chapters makes this 512-page title an introductory book.

Target Audience

Looks like there are two major audiences and reading patterns for this book: those wanting to fix their systems ASAP and thus using Exploiting Software as a reference, and those using it as a text book to learn about security. I've discussed the organization of the book above, and the reference types will probably be more interested in patterns and examples. For a casual reader (although casual readers wouldn't generally pick up a title with C++, Perl, ASM and hex dumps spread around the chapters) this is a book with great educational value, from two authors who have discovered numerous security vulnerabilities themselves.

Exploiting Software is not an easy title to read. Addison-Wesley shipped me the manuscript copy a month before it hit the bookshelves in its final version, and I found myself going through about two pages an hour. The authors bring up sometimes unfamiliar Win32 APIs and occasionally use ready-made tools available on the Web, so generally I found myself visiting MSDN and Google a lot to read through available documentation and download the latest version of the tools used. The book doesn't come with a CD. Some of the stuff, like inserting a malicious BGP packet to exploit a Cisco router (p. 281) is not really testable at home, and I have some reservations about verifying the example with my employer's routers.

The book is probably apt for 2nd or 3rd year computer science students and above. Besides the variety of languages that I mentioned above, you need to be familiar with the basics of Intel architecture, and generally be fluent with terminology like "buffer," "stack," "syscall," "rootkit," etc., as this is not an "Introduction to..." title. From my experience, you probably won't read it from page 1 to page 512 understanding everything perfectly, but for anyone interested in security and those making a career in software development it looks like a bookshelf must-have.

I interviewed Gary McGraw on the current state of software security, the relevance of the topic to the issues beyond C/C++ and improper buffer usage, and future directions in security. Network World magazine also ran an interview with the McGraw in which he talks about the reception of the book at the RSA Conference, whether the economics is right to invest in building secure systems, and whether his book does more harm by providing a compendium of known exploits.

Alex has written numerous reviews of other software and security titles. You can read more of his opinions at his Web site. You can purchase Exploiting Software: How to Break Code from bn.com. Slashdot welcomes readers' book reviews -- to see your own review here, read the book review guidelines, then visit the submission page.

Comments

poetry in motion

[tomstdenis]

Why I love Bruce...

"We wouldn't have to spend so much time, money and effort on network security if we didn't have such bad software security."

Is to smart as

"We wouldn't have some many crumbling roads if heavy vehicles didn't drive on them"

Is to insightful. I still say the best way to experience Bruce's mind in action is in person. In his books he's trying to pander to the market [of let's face it less than apt people] and in person he's talking with fairly brilliant people [e.g. me ;-)]

Tom

Re:poetry in motion

[Anonymous Coward]

Looks like someone flunked the analogy sectin on the SATs. Actually what he said is more like,

"We wouldn't have to spend so much money fixing roads if we would just build more resiliant roads in the first place"

Which is perfectly true. Sure it's not groundbreaking, but then it's not meant to be. The difficult job for quality insurance people is just to make people like you shut up and actually change the problem behaviors.

Re:poetry in motion

[Tjebbe]

And here we see that analogies, like code, are hard to get right the first time (or the second).

Re:But does it cover...

[IO ERROR]

This is where input validation comes in. Check every input value for sanity. Do something reasonable if the value isn't sane. How often have you forgotten to write error checking or input validation code? Do you check the return value from printf()? (yes, it has one) Every time? (I doubt it)

Writing bulletproof software is TEDIOUS. You still have to verify everything, and still somebody's going to find the one thing you missed and exploit the hell out of it...

Let the environment help us

[Lucky Kevin]

We need to use more intelligent environments to protect us from ourselves (and other less good proogrammers :-)).
Like the security manager in Java and the security "taint" stuff in Perl.

Re:...and would this be useful for the newbie code

[Ytsejam-03]

I would hope that no one lets a newbie coder get his grimy little paws anywhere near code that requires a careful consideration of security.

Everyone writing code should be giving careful consideration to security. In my experience few developers do, but that number is increasing...

Re:But does it cover...

[SphericalCrusher]

Exactly. Even though I may pick this book up for a good read, I can already say that a good 50% of hacking is not technical.

The social engineer shows just how easy it is to obtain information from someone than it is to actually copy it from their computer. Just by dressing proper and knowing the correct lingo, you could easily masquarade as an employee for the company.

Read The Art of Deception, by Kevin Mitnick. Great read indeed.

Re:Unreasonable expectations.

[maxwell demon]

I think his point is that they are not in such an environment any more, due to the internet. That is, your office desk is now at some public place, with lots of people who'd really like to get in. A place for which it wasn't designed, and for which the security doesn't suffice any more.

I liked

[g0bshiTe]

Hacking: The Art of Exploitation
It provided these same thoughts on software design, but also delved into more the ASM side of things. The book went on to state that "there is no such thing as secure code." I believe this statement to be true. With the current patch n sniff state of Windows, it is very easy to overflow a buffer to execute code. I have oft heard someone say my pc is unhackable, I run blah firewall, or X N.A.T. the sad fact is they are as easy to compromise as an unsecured network pc is. With the plethora of IE and other browser vulnerabilities out there you don't need to drive a tank through the front door. Seems though Microsoft left a Window open.

Re:Writing is bad enough, testing is worse

[Greyfox]

I did security auditing in a standard C library in a previous job. We wrote customized automated test for every freaking C library function. Not only did we document potential side effects from each one of those functions, we could run the entire test suite whenever modifications were made to the library to insure that everything still worked as expected. That job was a real eye-opener, let me tell you...

Little things can make a big difference too. Let me give you a hypothetical; Lets say the AIX standard C library strlen() tests its input to make sure it's not a NULL pointer prior to testing the string. Lets further say that the Gnu C library doesn't make this test. Recompiling your AUX application on Linux would potentially introduce crashes whenever your application encrounters a strlen.

While the above was a hypothetical situation, I have uncovered a good many memory overflows and leaks simply by compiling and running an application on a different flavor of UNIX than it was originally written for. Having safe underlying library calls is nice, but it also introduces the possibility that actual errors will go unnoticed for a longer period of time.

I'm pretty well convinced that in a situation where the need for security is high (Say, for example, an OS kernel) documented testing of every single function that makes up the software is a necessity.

The other half of the problem

[Brandybuck]

There's another side to the problem. It's insidious. And while Microsoft is fully embedded in this tar pit of insecurity, Open Source projects are rarely better.

This problem is "feature requests from users." If very few developers understand security well enough to write secure code, think about how much less end users know. Yet it is the end user who pays us. They're our ultimate boss, even on the free-beer Open Source side of things.

At work I've had feature requirements come to me from marketing that would absolutely eviscerate the product's security. I've also seen bug reports elevated to top priority that that would reduce or eliminate product security.

Here are some hypothetical (I hope) examples to show the dangers of this in the Open Source arena. While some of these might have been absurd a few years ago, with today's hyper-concern of usability, it wouldn't surprise me if they actually got implemented.

"It's too much work changing file permissions by hand, so we need a way to automatically execute arbitrary files."

"It's too much work remembering passwords, or remembering the master password for a password manager, so there needs to be a daemon running that will remember for us."

"Messages in XYZ email client should be automatically rendered in HTML/CSS/Javascript."

"The interface is too cluttered! Hide file name extensions!"

Or my all time favorite...

"Linux needs a InstallShield clone!"