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.

I’m sure you already know about the other “network management” – where ISPs and carriers get their hands publicly slapped for limiting bandwidth to high-traffic offenders. But when is this kind of “network management” a good thing? At a panel sponsored by the FCC in DC, reps from carriers and ISPs discussed what steps they’ve been taking to prepare for a pandemic or other major global crisis – that would force workers to stay at home or work from more remote locations to limit exposure.

Are people paying attention to ICANN? They’re saying that IPv4 will be fully allocated in the next two or three years. Does anyone care? In their bid to make people care, ICANN talks about the state of IPv6 adoption and touts Africa as the most rapid adopter.

SOA soon part of the ‘cloud’? No, please no.

Microsoft – The Silver Lining in Every Cloud. Joe Wilcox over at eWeek’s Microsoft Watch, has been following Steve Ballmer around and collecting some nice quotes on how the company is transitioning. “For many years, we had kind of what I would call the all-encompassing mission, vision and scorecard statement: a computer on every desk and in every home. …Well, our footprint and portfolio is broader than that. “ [In every hand and of course, in every cloud…] “So, as a vision statement we talk about creating seamless experiences that combine the magic of software, the power of the Internet across a world of devices.” The magic of software – something I haven’t thought about for a while. And:

“You need a real platform in the cloud. When we wanted to go after the PC, we built an operating system. When we wanted to go after the phone, we built an operating system. When we wanted to go after the enterprise, we built an operating system. We’ll announce a new operating system, one that runs in the cloud and has a wide variety of capabilities.”

On the other hand, it's probably a smart idea to screen screeners when they walk through airport security when they aren't working at that checkpoint at that time. The reason is the same reason you should screen everyone, including pilots who can crash their plane: you're not screening screeners (or pilots), you're screening people wearing screener (or pilot) uniforms and carrying screener (or pilot) IDs. You can either train your screeners to recognize authentic uniforms and IDs, or you can just screen everybody. The latter is just easier.

I think a good litmus test of the mental and moral quality at any large institution [with significant derivatives exposure] would be to ask them, "Do you really understand your derivatives book?" Anyone who says yes is either crazy or lying.

It is crazy to allow things to get too big to fail, run with knavery. As an industry, there is a crazy culture of greed and overreaching and overconfidence trading algorithms. It is demented to allow derivative trading such that clearance risks are embedded in system. Assets are all “good until reached for” on balance sheets. We had $400m of that at general re, “good until reached for”. In drug business you must prove it is good. It is a crazy culture, and to some extent an evil culture. Accounting people really failed us. Accounting standards ought to be dealt with like engineering standards.

There are distinct parallels between phishing / retail payments, and the bigger investment mess. In both cases, banks would argue these are core business. In both cases, they have applied risk-based security models, and accepted some loss. In both cases, they have the ability to apply substantial experience to the monitoring, allocating and absorbing risks and losses.

In both cases, they watched and did nothing as the risks started from low, and migrated upwards. Are we at the point where regulation has killed the ability of banks to apply their (arguable) one core skill, to whit, risk-based analysis? Are banks that far out of banking that they no longer have it?

So, a company that I met with had a problem. This was not a ginormous problem itself, but rather it was an awakening to a new threat that had not emerged as public enemy number one before. Its employees. It so happens that this company has the best security that King Arthur could buy, but it's not being used right and someone thought it would be pretty clever to crash a database server and see what would happen. Or did they? Or was it the computer playing a practical joke? HAL, anyone?

It turns out this company handles sensitive information about its customers, and yet they don't know WHO DONE IT or WHY?...]]> Mon, 08 Sep 2008 10:00:00 +0000 casual hack public enemy company database server practical joke pretty clever employees ginormous hal When there's something strange in the neighborhood, who you gonna call? http://securityratty.com/article/7f9e569822e0521bce9615d70124032f http://securityratty.com/article/7f9e569822e0521bce9615d70124032f Today I will discuss a general approach to model air traffic control (ATC) using our CEP/EP reference architecture which is an application of the mature JDL multisensor data fusion model.

ATC is an excellent working example of complex event processing.   Radar and GPS provide the basic sensory information to accurately track and trace the position of each aircraft in the area of responsibility (AOR) of a particular control tower/zone.     Naturally,  sensory information is preprocessed and formatted in such a way that the data can be processed upstream by multiple real-time applications.

Before we look at complex ATC scenarios, such as “potential collision” or “aircraft off approach vector” we must trace and trace individual objects, aircraft-objects, accurately with very high confidence.    In addition to tracking aircraft-objects, there is a database of information about the aircraft (ideally), such as make, model, age, range, passengers and other properties about the aircraft-object.      In addition, there is a state-model for each aircraft, for example the aircraft might be “on the ground”, “approaching the runway”, “cleared for takeoff”, “cruising altitude”, “approaching runway”, “final decent” etc.  

Tracking and tracing individual aircraft is what is generally referred to as “object refinement” in our CEP/EP reference architecture.   The reason we call this function “object refinement” is that system engineers are focused on optimizing the situational knowledge about individual objects.     Sometimes we refer to this function as “track and trace” because that is what we are doing to  each object in the model.  In Marc Adler’s recent shoplifting scenario, Marc was interested in tracking and tracing people in a store using imaging processing techniques to estimate their behavioral patterns.  In the same way, before we can process for scenarios such as “potential shoplifter” or “suspicious criminal gang activity” we must be able to accurately process (track and trace) individual object, such as people or merchandise.

Back to aircraft and ATC, the “complex event processing” begins when we are looking about object-object relationships, in this model, aircraft-to-aircraft, but this is an overly simplistic model, as we have not yet added (to our model) ground features (towers, buildings, power lines), weather (storm cells, wind) and other flying objects (known migratory bird paths, swarms of insects) to our simple model.  

Complex event processing occurs when we are processing multiple objects in our model looking for threats in real-time.     Practically speaking, all ATC applications are CEP applications.  This means that vendors and integrators who build ATC applications are also CEP vendors.   

Editorial Note: CEP/EP has been around for a long time and was not recently invented in the past decade as some “inventors” would like for us to believe. 

As you can imagine, there is considerable “complex event processing” that goes on “behind the scenes” to provide air traffic controllers and pilots situational knowledge into the “friendly skies”.   As you might further imagine, the situation is more complex when the skies are “not so friendly”, for example, in air combat situations.   

Processing myriad objects is not the end of the processing “chain”.  For example, decisions are being made constantly about potential damage, alternative airports, and more.    In our reference model, we refer to this, generally speaking, as “impact assessment” because we must take an estimated detected complex event, for example “aircraft collision,” and estimate potential damage based on numerous factors such as, the amount of jet fuel in the aircrafts and the location of the aircrafts (over a large city or rural area, near a hospital and emergency services).   Regardless of the scenario, an impact assessment is normally required before optimal decisions can be made.

This is true, by the way, for our shoplifting example (the impact is different if a piece of gum is stolen versus a $1,000,000 diamond necklace or weapons-grade nuclear material) and other scenarios and models.  Static data (information about objects) is required for accurate decision processing.  

Impact assessment is not the end of the “knowledge chain”.    Decisions are constantly being made that effect resources.  For example, suggestion an alternative route for an aircraft is a resource management decision.    Turning on and off radar or switching to alternative tracking devices is a resource management function.  In our CEP/EP reference model (based on the JDL data fusion model), we call this “resource management”.   This function includes contacting emergency services and directing them to a potential crash location or sending out a message to instruct all aircraft to stay off a certain radio frequency.  Resource management is critical.

Our simple ATC model today is by no means complete, it just scratches the surface.  In fact, I have a very close friend, Mark Secrist, who is a former Marine fighter pilot and currently a senior captain for American Airlines.   I have asked Mark to read this post and help me further refine this crude “laymans” ATC model (Thanks Mark!).