No doubt you are aware of the out-of-band security bulletin issued by the Microsoft Security Response Center today, and like all security vulnerabilities, this is a vulnerability we can learn from and, if necessary, can use to shape future versions of the Security Development Lifecycle (SDL).

Before I get into some of the details, it's important to understand that the SDL is designed as a multi-pronged security process to help systemically reduce security vulnerabilities. In theory, if one facet of the SDL process fails to prevent or catch a bug, then some other facet should prevent or catch the bug. The SDL also mandates the use of security defenses, because we know full well that the SDL process will never catch all security bugs. As we have said many times, the goal of the SDL is to "Reduce vulnerabilities, and reduce the severity of what's missed."

In this post, I want to focus on the SDL-required code analysis, code review, fuzzing and compiler and operating system defenses and how they fared.

Code Analysis and Review

I want to start by analyzing the code to understand why we did not find this bug through manual code review nor through the use of our static analysis tools. First, the code in question is reasonably complex code to canonicalize path names; for example, strip out ‘..' characters and such to arrive at the simplest possible directory name. The bug is a stack-based buffer overflow inside a loop; finding buffer overruns in loops, especially complex loops, is difficult to detect with a high degree of probability without producing many false positives. At a later date I will publish more of the source code for the function.

The loop inside the function walks along an incoming string to determine if a character in the path might be a dot, dot-dot, slash or backslash and if it is then applies canonicalization algorithms.

The irony of the bug is it occurs while calling a bounded function call:

_tcscpy_s(previousLastSlash, pBufferEnd - previousLastSlash, ptr + 2);

This function is a macro that expands to wcscpy_s(dest, len, source); technically, the bug is not in the call to wcscpy_s, but it's in the way the arguments are calculated. As I alluded to, all three arguments are highly dynamic and constantly updated within the while() loop. There is a great deal of pointer arithmetic in this loop. Without going into all the gory attack details, given a specific path, and after the while() loop has been passed through a few times, the pointer, previousLastSlash, gets clobbered.

In my opinion, hand reviewing this code and successfully finding this bug would require a great deal of skill and luck. So what about tools?  It's very difficult to design an algorithm which can analyze C or C++ code for these sorts of errors.  The possible variable states grows very, very quickly.  It's even more difficult to take such algorithms and scale them to non-trivial code bases. This is made more complex as the function accepts a highly variable argument, it's not like the argument is the value 1, 2 or 3! Our present toolset does not catch this bug.

Ok, now I'm really going out on a limb with this next section.

Over the last year or so I've noticed that the security vulnerabilities across Microsoft, but most noticeably in Windows have become bugs of a class I call "onesey - twosies" in other words, one-off bugs. There is a good side and a bad side to this. First the good news; I think perhaps we have removed a good number of the low-hanging security vulnerabilities from many of our products, especially the newer code. The bad news is, we'll continue to have vulnerabilities because you cannot train a developer to hunt for unique bugs, and creating tools to find such bugs is also hard to do without incurring an incredible volume of false positives. With all that said, I will add detail about one-off bugs to our internal education; I think it's important to make people aware that even with great tools and great security-savvy engineers, there are still bugs that are very hard to find.

Fuzz Testing

I'll be blunt; our fuzz tests did not catch this and they should have. So we are going back to our fuzzing algorithms and libraries to update them accordingly. For what it's worth, we constantly update our fuzz testing heuristics and rules, so this bug is not unique.

Defenses

If you want the full details of the defenses, and how they come into play on Windows Vista and Windows Server 2008, I urge you to read teh SVRD team's in-depth analysis once it is posted.

A big focus of the SDL is to define and require defenses because we have no allusions about finding or preventing all security vulnerabilities by attempting to get the code right all the time, because no-one can do that. No one.  See my comment above about one-off bugs!

Let's look at each SDL mandated requirement and how they fared in light of this vulnerability.

-GS

The -GS story is not so simple. A lot of code is executed before a cookie check is made and the attacker can control the overflow because the overflow starts at an offset before the stack buffer, rather than at the stack buffer itself. So the attacker can overwrite other frames on the call stack, corresponding to functions that return before a cookie check is made. That's a long way of saying that -GS was not meant to prevent this type of scenarios.

ASLR and NX

The code fully complies with the SDL, and is linked with /DYNAMICBASE and /NXCOMPAT on Windows Vista and Windows Server 2008. There are great defenses when used together, and reduce the chance of a successful attack substantially. Also, the stack offset is randomized too, making a deterministic attack even more unlikely.

Service Restart Policy

By default the affected service is marked to restart only twice after a crash on Windows Vista and Windows Server 2008, which means the attacker has only two attempts to get the attack right. Prior to Windows Vista, the attacker has unlimited attempts because the service restarts indefinitely.

Authentication

Thanks to mandatory integrity control (MIC) settings (which comes courtesy of UAC) the networking endpoint that leads to the vulnerable code requires authentication on Windows Vista and Windows Server 2008 by default. Prior to Windows Vista, the end point is always anonymous, so anyone can attack it, so long as the attacker can traverse the firewall. This is a great example of SDL's focus on attack surface reduction; requiring authentication means the number of attackers that can access the entry point is dramatically reduced.

Firewall

We enabled the firewall by default in Windows XP SP2 and later, this was a direct learning from the Blaster worm. By default, ports 139 and 445 are not opened to the Internet on Windows XP SP2, Windows Vista and Windows Server 2008.

Summary

The $64,000 question we ask ourselves when we issue any bulletin is "did SDL fail?" and the answer in this case is categorically "No!" No because as I said earlier the goal of the SDL is "Reduce vulnerabilities, and reduce the severity of what you miss." Windows Vista and Windows Server 2008 customers are protected by the defenses in the operating system that have been crafted in part by the SDL. The development team who built the affected component compiled and linked with the appropriate settings as described in "Windows Vista ISV Security" and Writing Secure Code for Windows Vista so that their service is protected by the operating system.

The team did not poke holes through the firewall unnecessarily, in accordance with the SDL.

The team reduced their attack surface, in accordance with the SDL, by requiring authenticated connections rather than anonymous connections by default.

We know that the SDL-mandated -GS has very strict heuristics so some functions are not protected by a stack cookie, but in this case, there is no buffer on the stack, so there will be no cookie. We know this. There are no plans to remedy this in the short term.

Fuzzing missed the bug, so we will update our fuzz testing heuristics, but we continually update our fuzzing heuristics anyway.

In short, based on what we know right now, Windows Vista and Windows Server 2008 customers are protected because of the SDL-mandated defenses in the operating system, and because the development team adhered to the letter of the SDL to take advantage of those defenses.

Chalk one up for Windows Vista and later and the SDL!

As usual, questions and comments are very welcome.

“In order to keep its products safe, Google has adopted a philosophy of 'security as a cultural value'. The programme includes mandatory security training for developers, a set of in-house security libraries, and code reviews both by Google developers and outside security researchers."

I think it is great that Google has a security program they are willing to talk about and I could not agree more with the ‘security as a cultural value’ philosophy. But isn’t there something really fundamental missing here? Design? There is a lot more to software engineering other than coding and testing.
 
The SDL has a very large set of implementation-related requirements, but there are many design-related requirements also.

Computer security experts have known since the early 1970s that you have to get the design right; and our experiences with the SDL over the last 5 years have taught us that you need to consider security and privacy (but remember, you have to ship too!) very early in the design phase and have a consistent end-to-end process if you truly hope to reduce vulnerabilities and create more secure software. This is how the SDL is helping to create ‘security as a cultural value’ at Microsoft.

We’ve seen a general trend downward in security vulnerabilities in Microsoft products, and the IBM X-Force 2008 mid-year report backs the assertion that we’re making progress; according to the report Microsoft’s share of total vulnerabilities decreased from 3.7% in 2007 (1st place) to 2.5% (that’s 2.5% for all Microsoft products; a more appropriate comparison might be Windows vs Linux vs Mac OSX, or SQL Server vs Oracle vs DB2) in the first 6 months of 2008 (3rd place.) This is an encouraging signal that the SDL is working on a large scale… of course, it might also show that vulnerability researchers are moving to easier targets, which, to me shows the SDL is working too.
 
What do you think?

Blogger: Ramon Krikken

The web browser is one of those peculiar pieces of software, having to accept input from arbitrary sources and then parse and render the data that is sent to it. Part of this it does by itself, and other parts are taken care of by handlers and plug-ins. In doing so, it displays hypertext, images, videos, and even runs active content like Flash, JavaScript, and ActiveX.

But however much we love the browser, we’ve also come to hate the myriad of vulnerabilities that affect it. Everything from cross-site scripting to remote code execution via maliciously formed animated cursor files and Flash content can make browsing a hazardous activity. The browser is sick, and that’s not desirable for a platform we use for important business and personal transactions.

Worsening the browser’s diagnosis is the recent paper from Mark Dowd and Alexander Sotirov, sub-titled “Setting back browser security by 10 years,” which discusses how to bypass Microsoft Vista’s memory protection capabilities with some added effort for the exploit designers. It’s not that all of the techniques are necessarily new, but the browser appears to be particularly vulnerable to easy exploitation.

Surprising? Not exactly, when we take into account that the browser is suffering from the same disease as the general purpose operating system: bloat and compatibility. We expect the browser to do ever more, but everything we used it for before still needs to work as if it were yesterday. It feels a bit like people insisting on using a cardboard box as a safe, and wondering why their money keeps getting stolen.

It’s not like we haven’t been working on the browser’s cure, though. There have been some improvements in the browsers themselves, the operating systems have also implemented compensating controls, but most of all, there has been an enormous push for securing the web applications that deliver the data in the first place. Unfortunately, the latter two won’t help secure the browser in the long run.

The first issue is that not all content will come from ‘nice’ servers, the second that the server can only make an educated guess on how a browser will parse and render a given set of data, and the third that operating system controls have their own limitations, whether by design or implementation (for example needing to re-compile existing code to enable certain protections.) The browser, in the end, has to be mostly responsible for keeping itself safe; the operating system must assist it in doing so.

So we’re in a pickle. The browser is sick (and the operating system is too), but it’s hard to cure it without a redesign that will undoubtedly impact compatibility, the ever-so-desired multi-functionality, or its ease of use. We can layer defenses by using web filtering in the enterprise environment, but in the end – for the consumer market in particular – we need to fix the browser itself. I can think of a few things I think might help:

• Some kind of site security policy  to restrict where the browser loads auxiliary content from, and which data it can ‘trust’, when loading a web page (I’d prefer mandatory enforcement, and adding an HTML tag to be able to indicate blocks of untrustworthy data.)
• Restricted compartments for plug-ins to run in, ensuring that their bugs cannot easily affect the whole browser.
• Better software development practices for the plug-ins and content parsers themselves, so that they’re less vulnerable, and compiled with the latest protection measures to begin with.

All of this means more work, and some of it means a lot of unhappy reactions when things stop working. Even then we will of course still have to deal with additional vulnerabilities, such as those that may be present in hardware, but we will at least have taken prudent steps to ‘find a cure.’

Blogger: Ramon Krikken

The web browser is one of those peculiar pieces of software, having to accept input from arbitrary sources and then parse and render the data that is sent to it. Part of this it does by itself, and other parts are taken care of by handlers and plug-ins. In doing so, it displays hypertext, images, videos, and even runs active content like Flash, JavaScript, and ActiveX.

But however much we love the browser, we???ve also come to hate the myriad of vulnerabilities that affect it. Everything from cross-site scripting to remote code execution via maliciously formed animated cursor files and Flash content can make browsing a hazardous activity. The browser is sick, and that???s not desirable for a platform we use for important business and personal transactions.

Worsening the browser???s diagnosis is the recent paper from Mark Dowd and Alexander Sotirov, sub-titled ???Setting back browser security by 10 years,??? which discusses how to bypass Microsoft Vista???s memory protection capabilities with some added effort for the exploit designers. It???s not that all of the techniques are necessarily new, but the browser appears to be particularly vulnerable to easy exploitation.

Surprising? Not exactly, when we take into account that the browser is suffering from the same disease as the general purpose operating system: bloat and compatibility. We expect the browser to do ever more, but everything we used it for before still needs to work as if it were yesterday. It feels a bit like people insisting on using a cardboard box as a safe, and wondering why their money keeps getting stolen.

It???s not like we haven???t been working on the browser???s cure, though. There have been some improvements in the browsers themselves, the operating systems have also implemented compensating controls, but most of all, there has been an enormous push for securing the web applications that deliver the data in the first place. Unfortunately, the latter two won???t help secure the browser in the long run.

The first issue is that not all content will come from ???nice??? servers, the second that the server can only make an educated guess on how a browser will parse and render a given set of data, and the third that operating system controls have their own limitations, whether by design or implementation (for example needing to re-compile existing code to enable certain protections.) The browser, in the end, has to be mostly responsible for keeping itself safe; the operating system must assist it in doing so.

So we???re in a pickle. The browser is sick (and the operating system is too), but it???s hard to cure it without a redesign that will undoubtedly impact compatibility, the ever-so-desired multi-functionality, or its ease of use. We can layer defenses by using web filtering in the enterprise environment, but in the end ??? for the consumer market in particular ??? we need to fix the browser itself. I can think of a few things I think might help:

• Some kind of site security policy  to restrict where the browser loads auxiliary content from, and which data it can ???trust???, when loading a web page (I???d prefer mandatory enforcement, and adding an HTML tag to be able to indicate blocks of untrustworthy data.)
• Restricted compartments for plug-ins to run in, ensuring that their bugs cannot easily affect the whole browser.
• Better software development practices for the plug-ins and content parsers themselves, so that they???re less vulnerable, and compiled with the latest protection measures to begin with.

All of this means more work, and some of it means a lot of unhappy reactions when things stop working. Even then we will of course still have to deal with additional vulnerabilities, such as those that may be present in hardware, but we will at least have taken prudent steps to ???find a cure.???

Now, ordinarily, forcing mandatory extra authentication like this you'd think is a good idea, and something that should be applauded... ]]> Wed, 30 Jul 2008 20:00:00 +0000 favourite spice girl data security measures financial services authority client investment managers mandatory extra authentication fsa secret questions city firm strong authentication "Off the Peg" Authentication can lead to an ill-fitting suit http://securityratty.com/article/8ccf3e65d2b1b8b72fdbe0860c092c80 http://securityratty.com/article/8ccf3e65d2b1b8b72fdbe0860c092c80          I have a note to all network hardware vendors…

Dear network vendor,

As someone that is forced to configure and implement security on your hardware, I would greatly appreciate stable code and properly functioning features. Unfortunately, I cannot always choose the hardware my customers are using in their infrastructure. However, if you would like for me to recommend they continue purchasing and using it, then the product must demonstrate to me that it is: capable, reliable, predictable and well-documented. If your product is not meeting these requirements, I’m forced to recommend other solutions to your (current) customer.

Stable Code. If I have to spend 2-6 hours per implementation working through your product’s bugs, and then must either spend time on a support call or spend time getting packet captures to prove to you it’s not working, I am not a happy camper because you’re slowing down my progress. Your customer is not happy because they’re paying for that time and I’m not cheap.

Features. Don’t publish in technical documentation that your product, or code can do something, only for me to find out later that it cannot. On-site in the middle of an implementation is not the time to architect Plan B. Let me know before, either through technical docs, white papers, best practices or release notes. I do read those. If you want to bend the truth, do it the marketing fluff, not my technical documents.

Documentation. If your product does do what you say it does, then please do document and explain the concepts and procedures. Examples are good, but explanations are mandatory. A correct CLI reference is always lovely as well. If there are got’chas or tricks, please also document those. Again, white papers or release notes are fine. Having to track down the one security engineer from your company that holds the magic key is not practical, nor scalable. Plus, he may be on vacation during my install, which would make me irate.

Support. If your product is not functioning or performing as expected, do NOT expect your customers to have a current maintenance contract to address a known issue or bug (or an un-known issue or bug for that matter). If they found a bug for you, you should probably give them a maintenance contract for a year… or two. If you don’t let us call support, I will find one of your pre-sales engineers and we will use him or her for post-sales support, which is not what you want them to do. But that’s your problem, not mine.

I believe that sums up the major issues. Specifically, I am interested in security, RADIUS, SSH, SNMP, DHCP and 802.1X functions. Before you add another bell or tweak another whistle, please make what you have works… consistently. That should be first, so it’s my Feature Request #1.

Respectfully,

jj

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