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

But does it cover...

[MalaclypseTheYounger]

Stupidity? Security is easy. Making software stupid-proof is hard.

A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools.

-- Douglas Adams

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...

Re:But does it cover...

[robslimo]

I agree that creating stupid-proof is difficult, but I'm not so quick to blow off the task of making software secure. One methodology I've not heard much talk about is testing with external software that tries to break the application (though there is at least one company who makes a such a product, eeye.com, I think). Just like any other aspect of ensuring robustness in software, testing is the next critical step after design.

So design it to be secure, then test it! Try to overrun buffers, throw illegal arguments and all around garbage input at it, some specifically designed and even more that are randomized. When it crashes or misbehaves, find out what trashed it and fix it up.

Design, test, test, test, test, test!

Re:But does it cover...

[dilettante]

Making software stupid-proof is also expensive.

Most programmers that i know who have an interest in security have already set up Windows or Linux boxes with known vulnerabilities and attempted to duplicate known exploits. But knowledge is, at best, half of the picture. In most commercial software endeavors, what's really important is convincing everyone along the chain of command that security is important. This seems like it should be simple, but security is one of those horizontal aspects of software development that adds considerably to the expense of system development, but doesn't add many new features.

Further complicating the problem is that even if someone were to develop an environment that attempted to prevent all of the problems caused by programmer errors, it would be horrendously complex and would likely kill performance. Until threat modeling and code inspections with an eye on security become commonplace, this problem will persist.

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.

...and would this be useful for the newbie coders?

[Penguinisto]

The one question that sticks out is yes, learning how something is exploited will help out a guy who already knows how to code (and has enough experience to look at an exploit from both sides of the attack), but what about the newbie coder who, more than anyone else, desperately needs to know how to code properly in the first place?

Someone ought to combine a guide for writing secure code, but with exploit examples that dissect it from both crack and code perspective. (does this book do that, perhaps? Maybe I missed it, but I didn;t see any indication of that in there...)

Good Reading

[Anonymous Coward]

While I've only read the sample chapter given out at the recent RSA conference, I found it to be extrememly interesting. Useful for those looking for ways to secure consulting gigs fixing blatant security flaws in common software (especially web apps)

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

[kneecarrot]

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.

Note: I did not post this anonymously so I MUST NOT be a troll.

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.

Can't build security on a weak foundation

[Theodrake]

I keep reading all these books about how to fix the holes in existing s/w. How to not build systems that are full of holes. It seems we need a decent foundation and its not C. The DoD tried with Ada to design a language that eliminates a lot of the coding mistakes, but it just wasn't embraced. It just seems we are attempting to layer security on top of an inherently insecure software language.

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...

Secure code in risky languages: Hard

[fuzzy12345]

If you've been around long enough to start seeing patterns in software flaws, keep asking yourself: "What misfeatures of the program's source language contributed to this flaw?"

Personally, I find that I rarely need to access the thirty-second element of a thirty element array, and I'd die happy if I never have to type for(i=0; i<offbyone; i++){ again.

I used to think that Perl with taint checking enabled was the cat's meow, but I'm now leaning towards Lisp. For the rest of you, is it fair to blame the programmer when his tools (which are supposed to make his life easier) fail him? Use better tools!

How Secure is Secure??

[Un0r1g1nal]

You can write up about security, and tell people to code properly and validate everything but there are always going to be either exceptionally skilled hackers or totally inept users who will be able to do something that you didn't think of, and cause problems.

Look at some of the breaches that have been published in the last few years, and then consider if they are the ones they published (usually because they caught the person who hacked them) how many more are unpublished, either because they couldn't catch the attacker, couldn't figure out how the hacker got in in the first place or because said attacker penetrated so deeply they didn't want to be embarresed by it.

But as a good point, it allows people to keep being employed in the network security industry :P So all in all it's a good thing...

The problem starts at management...

[kbonin]

I write security software for a living, occasionally. I'm back in it now, after leaving it for a while out of frustration, among other things.

The problem is that even for us security geeks, its nearly impossible to get management to buy into spending the time to make things secure. Nobody would believe the stories I could tell about having security features gutted 'cause marketing decided certificates were too complicated, or 'cause access control systems were too hard to use, so "just put the built in passwords back in", or "*** wants a copy of the private keys", or "*** told me to tell you to check the private keys into version control". Stupid, stupid...

Until companies start caring about making products that are ACTUALLY secure, instead of just hiring security geeks to act as figureheads, then not letting them do their jobs, then system will continue to get hacked.

Sounds interesting

[plcurechax]

It sounds like I thought I was getting when I bought Hacking: The Art of Exploitation by Jon Erickson, which is fairly basic and easy to read level, other than some of the writing is not as polished as it could be. It did get through the basic concepts explained in various classic Phrack articles but without the 'leet speak which drives me crazy.

It sounds like this is a more serious and rigious book, and those that were turned off of Jon Erickson's Hacking might prefer it. I think I will take a look at it.

I think new programmers are likely better served reading something like Writing Secure Code: Practical Strategies and Proven Techniques for Building Secure Applications in a Networked World by Michael Howard and David LeBlanc or Building Secure Software by John Viega than get bogged down in details of this book.

Writing is bad enough, testing is worse

[RLW]

It is true that writing bulletproof software is TEDIOUS. However, after watching our test staff I have determined that testing it is beyond tedious. It is mind numbing!

The company I work for makes software for wafer fabrication. If the software fails, no one dies but millions of dollars of materials and time can be lost: we spend a lot of time testing and retesting and verifying our tests and going over scenarios to make sure we get it right. Event with all that, over the last couple of years we've logged over 600+ defects of various types. All the way from a misspelled word on an error message to miss-processed data to crashes. Most of those errors are detected in house and the customer doesn't see them: but I would guess we get 4 to 8 defects reported from customers every month with most being minor but a few are so egregiously bad that should have been impossible for that to make it through testing. But even a small error can cost tens of thousands of dollars or more in losses so no bug is a good bug.
Most other places I've worked have testing in name only. The code is compiled and run for a few seconds: some edit boxes are typed into and the mouse is wiggled around and that's it.

If architects make buildings like programmers write code then every woodpecker that comes along destroys civilization.

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.

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.

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!"