Building Secure Software 113
Building Secure Software: How to Avoid Security Problems the Right Way | |
author | John Viega, Gary McGraw |
pages | 528 |
publisher | Addison-Wesley |
rating | 8.5 |
reviewer | greg pryzby |
ISBN | 0201-72152-X |
summary | Good information for anyone involved with the creation of software which should be secure. |
BSS:HtASPtRW should be available at your favorite book outlet. It is available in hard cover from Addison-Wesley Professional Computing Series (white cover with blue strip). Since it is a security book, the forward is by Bruce Schneier and displayed on the cover. When you open the book, there are three pages of "Advanced Praise" for the book. So, the stage is set and the expectations are high. Will the book live up to the hype? I thought so.
Who should read the book? Anyone who cares about security. There is information for the manager, coder and everyone in between. Throughout the book, there are plenty of examples which I found very useful. John and Gary use code to show th at what they are talking about is not 'just theory'. That is right, there is code that shows the problems. That means samples of bad code, 'secure' code and code to show exploits.
I decided to look at a few chapters and talk about them specifically. Why did I pick these chapters? Because I found them interesting and thought others would too. I can't cover each chapter because I want John and Gary to write more books , so they need to sell a few copies!
Why do they do this? Isn't this giving the bad guys what they need? The bad guys have the information already. There is belief in the security community of full disclosure. This means not keeping things security and calling it secure. "Full disclosure means that hackers publicly disseminate information about your security problem, usually including a program that can be used to exploit it (sometimes even remotely)." (page 81)
Chapter 7 is on buffer overflows. I have read about buffer overflows for years. The chapter starts by explaining what a buffer overflow is and why it is a problem (pointy headed manager stuff). At this point John and Gary talk about how to protect yourself from buffer overflows. They start by listing problems in C and show why it is a problem. A list of functions that are 'bad' are given, but as any list, this isn't comprehensive. While avoiding the list is a good idea, you need to read why the calls are a problem so you can think about any call you use and why there maybe a buffer overflow.
The chapter then turns very technical. The difference between a heap and stack o verflow is discussed. An example is given that takes a C program and shows how to smash the heap and then how to smash the stack. This is pretty technical stuff , but very interesting. Finally an exploit is given. Very informative.
Chapter 9 is on race conditions. Time-of-check, Time-of-use (TOCTOU) is used to demonstrate a race condition. There is discussion on what a race condition is. John and Gary again step through code that is vulnerable and explain why it is vulnerable. Of course they show you how to write the code securely.
Chapter 10 is on randomness and determinism and lives up the the others. I know that random() isn't really random, is a pseudo-random number generator and should not be used when you need a real randomness. John and Gary give a great example to show how an online gambling poker application was open to cheating. Using some math and educated guessing, a GUI was written that would show you everyone's hand and how to win.
The next part of the chapter talks about how to generate randomness via software and hardware solutions. A discussion on entropy and how to determine the amount of entropy from the random source is given. Things get technical (I think), but you can follow the details or skim them. Regardless of how you decide to read this section, you will walk away with a better understanding of the problem.
I hope from the chapters I discuss, your curiosity has been peaked and you pick up a copy. There is other interesting stuff, like the 10 guiding principles for software security.
Web Resources
The web site recently was overhauled. The code from the book is
there as well are web resources. It is worth it to
take a look at
the web site for more information and to get a feel for the
information the book covers.
Contents
Foreword
Preface
Acknowledgments
- Introduction to Software Security
- Managing Software Security Risk
- Selecting Technologies
- On Open Source and Closed Source
- Guiding Principles for Software Security
- Auditing Software
- Buffer Overflows
- Access Control
- Race Conditions
- Randomness and Determination
- Applying Cryptography
- Trust Management and Input Validation
- Password Authentication
- Database Security
- Client-side Security
- Through the Firewall
Appendix A. Cryptography Basics
References
Index
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*runs to post office* (Score:4, Funny)
Re:*runs to post office* (Score:1)
Re:*runs to post office* (Score:2, Funny)
Re:*runs to post office* (Score:3, Funny)
The Windows User Interface Guidelines for Software Design, Microsoft Press.
Quote from book: "consistency makes the interface familiar and predictable".
Referenced from the Interface Hall of Shame. [iarchitect.com]
Re:*runs to post office* (Score:1)
Apparently, you didn't see the article a while back on Writing secure Code from MSPress
Those who have looked at the book seem to come to the conclusion that the knowledge necessary for writing secure code must apparently exist at Redmond, but something besides the total lack of knowledge is what is driving security problems there.
Random Numbers (Score:2, Informative)
Re:Random Numbers (Score:3, Interesting)
This can be very hard to determine. Here [keio.ac.jp] is a random number generator with period 2^19937-1. Presumably it could be modified to support a larger period.
Re:Random Numbers (Score:1)
PGP/GnuPG use this method, and if I'm not mistaken, so does the Linux kernel (to feed /dev/(u)random).
Re:Random Numbers (Score:2)
I have a hard time believing this... You're seriously implying that Linux servers (no keyboard) have an inferior /dev/urandom?
Re:Random Numbers (Score:2)
> seriously implying that Linux servers (no
> keyboard) have an inferior
That's true, actually. Check out
/dev/urandom uses all sorts of hardware timings (like incoming packets, hard drive seeks, etc.) to produce add entropy to its pool. Typing or moving the mouse improves this, though I think "inferior" might be too strong a word since they are both nearly unpredictable anyway.
Re:Random Numbers (Score:2)
Re:Random Numbers (Score:2, Insightful)
You will probably come back with some retort about chaos theory and the formation of patterns, so let me tell you what's wrong with that idea right now: Chaos theory does say that in many cases, "random" data will form identifiable patterns. However, often those patterns are not distinct over a small sample. Even given a few million numbers from a sophisticated random number generator, you would be hard-pressed to come up with a pattern in them - even using incredible amounts of computing power. This is why the NSA was so scared of things like PGP a few years back (and still are!). In short, the world is definately not "un-random", especially in very small domains -- such as those microprocessors operate in.
Re:Random Numbers (Score:2, Informative)
If all CPUs implemented something similar then can true random numbers be obtained from that?
Truely Random Numbers from Intel (Score:2)
--Mike--
Re:Truely Random Numbers from Intel (Score:1)
Re:Random Numbers (Score:2)
Speaking of rand() [OT] (Score:1)
I'm taking an Intro to C++ course, and the assignment is to roll two dice, add the results, and keep track of the frequency of each result from 2-12. Easy right?
I've got a function called roll() that returns (rand()%6)+1, and then in main I have a loop that does "results[roll()+roll()]++" 36000 times.
Pretty straight forward program, and works as expected compiling under Metrowerks on Windows and gcc on a Linux box, but under cygnus (egcs 2.91.57) all of the results are odd. In other words, only 3,5,7,9,11 have any results, the evens are completely skipped.
Added in some cout's to see what was happening, and the roll()'s were alternating, without fail, between even and odd results - all numbers 1-6 were present, but they marched lockstep even-odd.
Presuming there was a problem in cygnus' implementation somewhere, the instructor proceeded to try it on a BSD box (with a later gcc - 2.95, I believe) with exactly the same result.
Searching on google proved fruitless (I was crushed!) - anyone know where I could get more info on this?
Re:Speaking of rand() [OT] (Score:1)
Re:Speaking of rand() [OT] (Score:1)
Re:Speaking of rand() [OT] (Score:3, Informative)
I saw an older manpage of rand() years ago, where they explicitely stated that the lowest bit would alternate and recommended only to use the high bits.
For a good PRNG check out the Mersenne-Twister [keio.ac.jp]
Re:Speaking of rand() [OT] (Score:1)
The C rand() function has very few requirements imposed on it. Implementations that alternate odd, even, odd, even, ... used to be very common, and there are still some around. This behavior is allowed by the standard. So, for truly random numbers, one should never use (rand() % n). There are warnings to this effect in the Linux man page for rand(3). At least in Debian.
Use random() and srandom() (instead of rand() and srand()) if you have them available. If not, you have to do a little bit of work. The basic idea is to use the result of rand() to produce a floating point value in the range [0.0, 1.0). Then you can multiply that by the width of the desired range, 6 in this case, to produce a value in the range [0.0, 6.0). Truncate that to an integer, producing one of {0, 1, 2, 3, 4, 5}. Then add the lowest value in the range, 1 in this case, to produce a one of {1, 2, 3, 4, 5, 6}. I don't think this is quite perfect; it seems that the highest value would be slightly less probable due to the limited resolution of floating the point. But I think it works in practice. Some code like this (warning, not thoroughly tested):
int rand_range(int low, int high)
{
return low + (int)((rand() / (RAND_MAX + 1.0)) * (high - low + 1));
}
And then, to roll a die, call it like this:
rand_range(1, 6);
HTH
Re:Speaking of rand() [OT] (Score:1)
Re:Speaking of rand() [OT] (Score:1)
Re:Speaking of rand() [OT] (Score:1)
Re:Random Numbers (Score:1)
in his youg days. As a true random numbers generator he
used white noise from the line imput of a sound card.
It looks like quite unpredictable.
Comments from author (Score:5, Informative)
Re:Comments from author (Score:2)
Just a heads-up for folk in the UK looking to buy this book - it-minds.com are doing it for £37.99, 10% off of list price. I think you have to go in via theregister.co.uk
amazon.co.uk have got it for £41.99
Re:Comments from author (Score:2)
It's on for a 15% discount at Readme.Doc [readmedoc.com] right now.
cost (Score:1)
BSS [bookpool.com]
Re:security vs. trade secret (Score:1, Informative)
People do not realize how easy it is to make changes to a program, or gleam its purpose/implementation from views of such code fragments.
The average copy protected game is hacked to undo the copy rotection in less than 2 days. Even if it is a new copy protection method.
Re:security vs. trade secret (Score:1)
Oh, and your "stat" about the average copy protected game being hacked in less than 2 days
Not that simple. (Score:2)
I wouldn't be surprised if black hat tools exist which can scan disassemblies for probable stack and buffer vulnerabilities. Where this gets tricky is figuring out enough of what that section of code does to craft an exploit. It is still less difficult than full blown reverse engineering. The process would be akin to finding cheats in MAME or looking for Nintendo cheats with a Game Genie. One way I can think of to ease that part of it is to rebuild the disassembled code so that it can be single stepped when executed. Something like Bochs could also be used so that the black hat investigator can monitor the execution environment to any level of granularity desired. Once it's known what functionality the suspect code implements, one can start coding prospective exploits.
Recreating a secret API would be FAR more difficult. An exploit is basically something that adds itself to already running code. One doesn't have to have extremely deep knowledge of what the vulnerable code does. A project like WINE attempts to replicate the functionality of that code in a source maintainable format. It's a whole 'nother kettle of fish altogether.
Engineered in (Score:5, Interesting)
For example, Freenet [freenetproject.org] starts with the assumption that nodes on the network will sometimes be hostile to the network, and that they will fail without reason. That fundamental assumption makes their network stronger IMHO than it would have been if they started with a blue-sky look at the network and added code to prevent certain types of attacks.
Also, it seems to me that security in applications is probably something won by hard experience. I'm not even sure if it's possible for somebody whose been hacking for just 1 year to build a fundamentally secure application, but trying to learn never hurts.
Re:Engineered in (Score:5, Informative)
Re:Engineered in (Score:1)
For an example of the results of engineered in vs. added on security, examine Unix and Windows. Unix was from the start a networked multiuser system, and security was paramount. Windows on the other hand was based on DOS which was originally intended for single user non-networked PC's. The result? *nix community worried about a better firewall and password protection, and MS creating a department of 'Security Assurance' to tell customers their software is secure no matter what the truth is.
So yes, designing security in from the beginning is important.
Great Read (Score:2, Funny)
Re:Great Read (Score:1)
Re:Great Read (Score:1)
Re:Great Read (Score:1)
He Rewrote the stories about Turambar, Beren & Luthien, and Earendel at least 3 complete times. IMHO these are the most important stories. The versions in Unfinished Tales are the best but they are, um, unfinished.
We now return you to your regularly scheduled program
Secure Programming for Linux and Unix HOWTO (Score:5, Informative)
My favorite:
http://www.dwheeler.com/secure-programs/ [dwheeler.com]
Re:Secure Programming for Linux and Unix HOWTO (Score:5, Informative)
Security is very important in today's software (Score:4, Interesting)
-Minus not followed by digit
It goes to show, it is easy to catch the under/overflows (and even that doesn't happen all to often) but writing good software is hard. This book is definitly going to be on my teachers wish list for this year.-several minus signs after each other
-minus preceded by a digit
Re:Security is very important in today's software (Score:2)
If so, I'm always surprised at how many people miss the common case of correctly parsing the most negative integer.
Praise grid for libraries, in this case.
Re:Security is very important in today's software (Score:1)
Re:Security is very important in today's software (Score:1)
Security is like Online Gaming. (Score:4, Insightful)
For security? Everyone and everything around you is a hax0r. Games? Everyone and everything around you cheats.
Look at a game like EverQuest. Are their cheaters? Certainly. Are nintey nine percent of the subscribers to EQ affected by them? Nope. The reason being, EQ realizes that to remain 'cheat free', it has to look at every aspect at the game that the design team proposes, and sit their thinking of ways that people might try to take advantage of and cheat with them.
Other games don't do this. The Diablo series, with duping/etc. Phantasy Star Online, with duping/illegal player killing/corruption of characters/etc. Half-Life and its mods, with spiked models/etc.
The result? Games which believe the player is guilty until proven innocent tend to remain, for the most part, cheat free. Those which don't end up ridden with so many cheaters that the game then becomes unplayable.
Security is the same way. If you think, "No one will do that." with your program, you've already lost. Because, in the end, someone will, just to be an ass.
As has been said quite a few times before, security isn't an option. It's not something that can be added as an afterthought. It's a vital part of the design process, and cannot be left out.
Software isn't the United States - remember, it's okay to design with the thought that all your users are malicious.
Re:Security is like Online Gaming. (Score:1)
Re:Security is like Online Gaming. (Score:1)
Many changes to the mod system are rejected because of the possibility for abuse (see the FAQ). Not to say it's perfect as it is, of course.
You're exactly right (Score:1)
Whats funny is that I designed Gnutella without knowing about it. I was designing an unhackable version of Diablo 1. Where characters are stored client side... The key was there was a psuedo server made up of the thousands of other people playing who also kept your data... It was a P2p network as base then everyone stored extra data... If you looked like you were cheating by a large % of computer police, then you're no longer in the network... This may sound shady and up for corruption, but online communities do flag people as shady to begin with... Its not really succeptable for conspiracy either because if you want to take your ball and go home, you can do it with your friends too.
Re:Security is like Online Gaming. (Score:1)
Well, it was. And so came ShowEQ. And much of the world that was supposed to be "hidden" isn't. ShowEQ gives a tremendous advantage, if only to show things like bugged monsters that won't path back to their home properly and will continue to interfere with pulls. More shady people use it to check on mob spawns in a zone. All of this is possible because during the design of EQ they chose to send the client information on EVERYTHING in the zone instead of just an area near you (this is also why EQ is broken into zones in the first place, and is largely an artifact of EQ's MUD origins and how old it is now).
They've gotten smarter though. They stopped sending the monster's hp's as a signed short and started sending it as a percentage (this also allowed them to exceed 32767 hp on monsters). They stopped sending the actual number associated with faction (-2000 to +2000) and started sending a number indicating level (0 = worst, 7 = best). Numerous other silly things like this, which should never have been in the datastream to the client in the first place, have been fixed.
Of course, there's still the gaping holes of spdat.eff (the Spell Data Effect file - lists every spell in the game and their effects), the fact that they send full item data over the wire when you inspect an item (including undisclosed stuff like haste percentage), they still send mana available for spell casters over the wire, and several other things.
The mantra of network game programming - don't trust the client - should be a mantra for most coding if you want it to be secure. And while you can attempt to patch crap afterwards, if you don't design it in from the start you will wind up with security holes that are too expensive to fix.
;) [lameness filter text] (Score:1)
Seminar By Author (Score:4, Informative)
It's hosted by the Centre For Applied Cryptography Research (CACR) [uwaterloo.ca] at the University of Waterloo. Anyone in southern Ontario who liked the book might consider attending.
Info:
Building Secure Software: How to Avoid Security Problems the Right Way
Gary McGraw, Cigital
Mar 20 (Wednesday), 2:30 pm, DC 1302
It's great that people are writing books like this (Score:1)
Security is a process (Score:3, Insightful)
Its a well known fact that security is a process, it should be considered right from the word go, and not just prior to a software release.
I've been writing a network server, recently, for streaming MP3's [gnump3d.org], so I been thinking a lot about the various issues.
I came up with a list of things that I should be doing, partly after reading bugtrack [securityfocus.com], and partly due to things I've picked up over the years.
I think its good to see books like this come out - if only to educate the newer/younger programmers who've never though about the issues before. After all many programmers just work on applications which aren't installed setuid, etc, so when they have to work on such a beast, for the first time, they're likely to work the way that they always have.
I believe that all the programmer courses available should have a section on security - largely because too many people learn from code printing in books, or online, which has all the error checking omitted, so the user can focus on the example. Its obvious from reading many peoples code that they never expect a malloc to fail!
BSS:HtASPtRW (Score:1)
Worst review ever! (Score:1, Insightful)
"I can't cover each chapter because I want John and Gary to write more books , so they need to sell a few copies!
Why do they do this? Isn't this giving the bad guys what they need? The bad guys have the information already. There is belief in the security community of full disclosure. This means not keeping things security and calling it secure. "Full disclosure means that hackers publicly disseminate information about your security problem, usually including a program that can be used to exploit it (sometimes even remotely)." (page 81)"
The first line here starts with a ridiculous comment about why the review is so short. Thanks for telling me you're lazy. Then, the review jumps to the middle of some paragraph that apparently only partially made it on the page. Why do they do what? Could someone please explain to me what "This means not keeping things security and calling it secure." means? I could go on to the rest of the paragraphs which are two line summaries rather than any analysis of quality, but the point is made.
We are a technical audience, and could have had a much more in-depth review without the nuances being lost on us. Even more so, PLEASE get an editor to at least LOOK at the reviews. Now I have to go elsewhere to find a review so that I can figure out whether or not this book is worth buying. The author's positive review sounds like it came right out of:
http://www.quartertothree.com/features/editorials/ lackey/game_reviews_gone_bad.shtml [quartertothree.com]
Re:Book review (Score:1, Flamebait)
Far too many to call out in detail.
Why don't you turn that Discerning Grammatical Eye toward your own writing next time?
Why do all security books concentrate on hackers? (Score:1)
I understand the majority of security breaks are perpetrated by people who are already authorized to use the software in question, but do so in a way not consistent with their job description, as if the only security was the job description.
Insiders, in other words.
I went looking for security books a while ago and found lots of books on how to secure your web server and keep your machine from getting rooted and how to encrypt data sent over the wire. Now I see a book with a chapter on buffer overruns.
How hard can it be to write a book on keeping the various legitimate users of the system from snooping around the parts of the system they aren't supposed to go to? Doesn't anybody remember the scandal at the dept of Health & Human Services (I think that's the right dept.) in which users of the system were essentially surfing people's social security data for entertainment? I don't believe that had anything to do with buffer overruns or rooting servers or any of that hacker shit.
Re:Why do all security books concentrate on hacker (Score:1)
The problem of malicious insiders is one that the software can only deal with up to a point. You need to have good physical security and good network security (e.g., strong passwords, etc.) I think it'd be good to see a book on defending against malicious insiders, but you can bet it will focus more on aspects other than the software security.
Re:Why do all security books concentrate on hacker (Score:1)
I just read it and it's great (atm, i'm reading BSS
Re:You can also just use a Virtual Machine (Score:1)
The strange thing is that buffer overflows are very old problems, and have been known for ages. Most (experienced) programmers also know how to avoid them, either by not using some functions blindly or using some form of boundchecking, but STILL they make up about half the security bugs found nowadays. It seems that some people just don't care...
If you do care then remember that the buffer overflow isn't the only security problem source, but just a common (and pretty stupid) one.
Re:You can also just use a Virtual Machine (Score:1)
examples corrupted (Score:1)
Har har :D (Score:2)
Quite an abbrevation, doncha think?
Abbreviations are supposed to be shorter than the word... how about BSS (Building Secure Software). One can normally omit the subtitle in an abbrevation
Moderators NB: This is intended as humor. The last bit (about an abbrevation suggestion) was tacked on 'cos it was a thought.
How to solve the buffer overflow problem.. (Score:1)
Recall that the way this usually works, is overwriting a return address through the non-bound-checked data with some function address that will execute a shell or something of the sort. If it's not on the data stack - you CAN'T overwrite it.
This will require changes both in compilers and in the instruction set, true. But it will make things inherently more secure. The worst one will be able to do with buffer overflow is corrupting data, but no NEW functionality will be executed.
More to the book? (Score:1)
Hopefully not, but from other reviews/stories I've seen here on
If that isn't the case, I would have really appreciated a more thorough review (beyond "I liked it").
Re:LOL! (Score:2, Informative)
Re:LOL! (Score:1)
Re:LOL! (Score:1)
Re:LOL! (Score:2, Informative)