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.

Richard Stallman - the man that gave us GNU - doesn’t trust Cloud providers with his data and says you shouldn’t either.  Richard believes we should store our private data on our own computers using ‘free’ (as in freedom) software.  The ironic part for Richard is that a significant portion of the Cloud is powered by open source software which he indirectly created (think gcc).

Richard sees it as a question of control.  Control is important but it isn’t the only variable.  Rather, I see it as a question of control, competence and economics.

The quick rebuttal to Richards’ view is this: the average computer user is not as smart as you.  Control is not the same as competence.  Control is about exercising choice, not about requiring everyone in the world to develop sufficient skills to protect complex hardware and software systems (aka their computer) against ever increasing threats.

My view is that privacy is not ‘free’.  It comes at a cost.  Whether you run your own systems or rely on someone else to do it, there is a cost.  There is cost in designing and implementing mechanisms to support privacy.  Beyond upfront costs there are ongoing expenditures to ensure privacy is maintained e.g. maintaining access control lists, testing and applying security patches, data leakage prevention etc.  None of these things are ‘free’.

If we agree that privacy costs money then how much is your privacy worth?

Stop for a second - think of a number…  

Now did we all think of the same number?

The problem with a one size fits all approach to privacy is that we each place a different value on it.

Checking in on the EPIC site, I saw this:  

A new report from Pew Internet and American Life Project indicates that “cloud computing” applications, such as web-based email and other web apps, are raising new privacy concerns. The report Use of Cloud Computing: Applications and Services found that 69% of online Americans use webmail services, store data online, or use software programs such as word processing applications whose functionality is located on the web. At the same time, “users report high levels of concern when presented with scenarios in which companies may put their data to uses of which they may not be aware.” For example, 90% of respondents said that they “would be very concerned if the company at which their data were stored sold it to another party,” 80% say “they would be very concerned if companies used their photos or other data in marketing campaigns,” and 68% of “users of at least one of the six cloud applications say they would be very concerned if companies who provided these services analyzed their information and then displayed ads to them based on their actions.”

What does that tell us?

The average (American) Internet user finds Cloud services convenient but has concerns about how their privacy might be affected by Cloud providers actions (duh!).  The survey identifies a lack of awareness in how private data is used in some consumer based Cloud services (consistent with web advertising awareness surveys).  

Unfortunately, the results of this survey are not very actionable.  The survey doesn’t mention whether these are all ‘free’ Cloud services (we can only assume they are) or ask the respondents what their expectations of privacy are and how much they would be willing to pay for different privacy assurance levels. 

On a sidenote, respondents were not asked if they had actually read the privacy agreement for the services they signed up to.  But the providers know if they did or not…  Or at least, they have the data to figure it out.  At sign up time they can measure the time between displaying the privacy agreement and the user clicking ‘I accept’.  If its just a few seconds then its pretty obvious there was more scrolling than reading going on.  But I think we can probably guess the answer without the data ;-).

I believe we need to be able to link expectation of privacy with cost.

• How much are you willing to pay for privacy?  What level of privacy assurance do you need?
• How much is your Cloud Provider paying to protect your privacy today?  What privacy services could they reasonably offer if they had customers willing to pay?  How might this compare with how you manage your private data on your home computer today?

The cynical view is that we expect privacy but don’t want to pay for it.  Its a bit like uptime - there is a parallel universe out there, where internal IT departments allegedly meet their 99.999% uptime SLAs, but when Gmail goes down, the Sergey Brin witchcraft dolls come out.

From a provider perspective, the “cost” of privacy invariably gets bundled under that line item called ‘Information Security’.  And don’t be fooled, the cost of privacy in reality is more than the salary of the person employed to be the privacy advocate (if there is one).  If we can’t see how much our providers are spending on our privacy then how can we judge if they are spending enough?  And what is enough?  And what can I get if I’m willing to pay a little extra?

Personally, I would rather we get some transparency around privacy costs and assessment of offerings.  However, without a sufficiently sized market of customers willing to pay for privacy assurance and Cloud Providers willing to be more open, I won’t hold my breath.

What about you?  Would you be prepared to pay for privacy?  Should providers be more transparent about what they do and don’t do and how they do it?
 
 

When a data owner's (a business) sensitive data is breached it is difficult to quantify the monetary loss. According to respectable survey sources, the average cost of sensitive data breach for a large size company is about $50,000. I am attempting here to think about this in simple mathametical terms:

There is a data breach. From the data owner's perspective the loss is:

Loss = Cost to protect data + Loss of business due to data theft aka cost of competitive disadvantage

From the data thief's perspective

Net Gain= [Cost of producing the data  *  Data freshness factor] - Cost to steal the data + Profit of business due to data aka gain of competitive advantage

From the above two equations it is very clear that this is not a zero sum game. There is a clear cost asymmetry for a data owner and for a data thief. When there is an asymmetry there is an opportunity. Data owner would not even know that the data is lost because the original copy of the data may be still intact - data thief could have simply copied the data. Data theft does not look like a car theft, there is no vacuum left behind. 

This motivates a data thief to keep the cost to steal low, steal highly valuable data that has a long shelf life and in a way that data owner will never even be aware of theft.

From a data thief's perspective, the cost to steal data if kept high would disincentive him. Moreover, Data freshness factor, i.e. how valuable this data is over period of time plays an important role. A good example is content of today's newspaper is hardly valuable tomorrow, but the content of newspaper two days ahead (if can be procured)would be invaluable. Data relevance is a function of time and other marketplace variables -  Data freshness Factor accounts for that variable. A good way to discourage data thief is to increase his/her cost to steal the data. There are other inferences from the above equation. If there exists no competitive advantage with the stolen data, hardly any thief would even venture to steal the data in the first place. If the cost of producing data is very low, then probably thief can just produce the data himself and would not attempt to steal the data. If the cost of theft is kept high, it would definitely deter the data thief from stealing data using technical mechanisms, then the data thief would exploit weak links in data security such as use of social engineering to get access to the data.

From data owner perspective protecting data becomes very important. How much would the owner be willing to spend? Not definitely the cost equal to cost of producing the data. 1% to 10% of cost of producing data is considered prudent. For a data owner it is difficult to estimate cost of data protection of a specific data, because it is not easy to chunkify data protection costs. Moreover, as Dan Geer says in his book, a data owner has to protect himself from number of intruders not just one.

It pays for a data owner to: be aware of data breaches (or data leaks), employ appropriate mechanisms to protect the data; the cost of protection which is fractional cost of the valuable data and enhance information security awareness of personnel who handle the data.

Data loss is not a zero sum game. The advantage is in favor of a data thief (data thieves rather). Data owner does not give much thought on the value of data unless there is a data theft. But, a data thief has every reason to think about economics of data theft before he acts to steal the data else data thief won't survive in this game and he is very well aware of his advantageous position.

Please withhold all serious and interesting wireless news until after Labor Day, 'kay?