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.

Abstract

Complex Event Detection (CED) is emerging as a key capability for many monitoring applications such as intrusion detection, sensorbased activity & phenomena tracking, and network monitoring. Existing CED solutions commonly assume centralized availability and processing of all relevant events, and thus incur significant overhead in distributed settings. In this paper, we present and evaluate communication efficient techniques that can efficiently perform CED across distributed event sources.

Our techniques are plan-based: we generate multi-step event acquisition and processing plans that leverage temporal relationships among events and event occurrence statistics to minimize event transmission costs, while meeting application-specific latency expectations. We present an optimal but exponential-time dynamic programming algorithm and two polynomial-time heuristic algorithms, as well as their extensions for detecting multiple complex events with common sub-expressions. We characterize the behavior and performance of our solutions via extensive experimentation on synthetic and real-world data sets using our prototype implementation.

Probabilistic Complex Event Triggering by Daisy Zhe Wang, Eirinaios Michelakis, and Liviu Tancau, Computer Science Division, University of California at Berkeley, Berkeley CA 94720, USA.

Abstract. Recently, wireless sensor devices have been widely deployed in various application settings (including environmental research, control systems, etc.). Because of the inherent unreliability of sensor readings, any kind of reasoning in sensor environments needs to carefully account for noise. The key goal of pcet is to build an infrastructure that can automatically infer and reason about the probabilities of triggered events, using a principled probabilistic model for the underlying sensor data. Through such probabilistic reasoning, pcet can incorporate uncertainly factors and make finer – grain decisions on event occurrences. This is achieved through the use of a Bayesian Network to directly model and exploit correlations across different sensors and the definition of a complex – event language, which allows users / applications to create hierarchies of higher-level events. As experimental results verify, pcet simplifies the development process and boosts the efficiency of any system dealing with inherently uncertain data streams.

Someone on the IE security team forwarded me a document that had additional details. So here, for your enjoyment, is a chart listing the default settings for each security level. To answer the newsgroup poster, "medium" and "medium-high" aren't the same.

About the formatting: to get it to fit within the width of the blog's text section, I've made some abbreviations.

In a few cases, the table shows a number rather than D or E or P; below the table is a description of each such entry.

At the very bottom of this post I've included the settings from the privacy tab, too.

Note: these settings reflect those for Internet Explorer 7 on Vista SP1. Please see the MDSN link above for differences between IE 6 and IE 7.

.NET Framework

.NET Framework-reliant components

     1 = High safety

ActiveX controls and plug-ins

Downloads

Enable .NET Framework setup

Miscellaneous

     1 = Prohibit downloads from software update channels
     2 = Cache content downloaded from software update channels
     3 = Automatically install software updates

Scripting

User authentication

     1 = Prompt the user for name and password
     2 = Automatic logon only in intranet zone
     3 = Automatic logon with current user name and password

Privacy settings (on the "Privacy" tab)

Italian free space optics test hits 1.2 terabits per second (in Italian, Google translation): Researchers in Pisa, Italy, along with colleagues from two Japanese institutions, crossed 1.2 Tbps in a test. Free space optics typically uses infrared lasers, and can work over a distance of kilometers.

More Canadian Wi-Fi health fears: This time in an island in Montréal. One of the concerned citizens: "This is something that is really under the radar. People do not know that long-term health hazards are associated with wireless technology." They don't know that because all verifiable, repeatable, well-conducted, academic tests so far indicate that there's no such health hazard associated with EMF. The concerned folks are raising an alarm about Wi-Fi being broadcast island wide, but are not paying attention, obviously, to the AM/FM radio, satellite radio, cellular, cordless, and thousand other wireless uses that are bombarding them right now, often at far higher signal levels.

Wi-Fi in a tub: I'm not going to say anything more.

QuickerTek adds antenna to 300 mW ExpressCard for MacBook Pro: Users of Apple's higher-end laptops can drop $200 to get a 300 mW Draft N (802.11n) ExpressCard and 5 dBi external antenna with a mounting clip. That's a lot of power, and it's important to recall that have a louder signal doesn't mean that distant base stations can necessarily hear you better. Draft N devices typically pair better listening (receive sensitivity) with higher transmission power, however.

Mac product ties location settings to Wi-Fi position: Centrix has updated its $29 Mac OS X location preferences program NetworkLocation to take advantage of Skyhook Wireless's Wi-Fi positioning data. You can now tie the package of settings that control what email account you use, iChat status, programs launched, disks mounted, and other factors, to where you're currently at.

Hackers getting a free T pass may be the least of our worries — local hackers-turned-security experts suggest RFID keycards, wireless networks and medical devices implanted in the body are also vulnerable to hacks.

At last week’s Defcon hacker convention in Las Vegas, a team of researchers showed it was possible to get information such as Social Security numbers and medical diagnoses, and change the settings on an implantable defibrillator by impersonating the computer it communicates with wirelessly. By doing so, a hacker could send a fatal shock to a patient’s heart, said William Maisel of the Beth Israel Deaconess Medical Center.

It is almost like things haven’t changed since the 90’s when the L0pht worked to change the mindset of security:

1. Don’t trust vendor claims around security
2. Attacks aren’t “theoretical”
3. Security by obscurity is no security

The L0pht worked as an independent security research think tank.  For us it was non-profit side job researching and publishing vulnerabilities in software and hardware.  We did it for our love of technology and published what we found out because purchasers and users of the vulnerable systems deserve to know.

It’s 10 years later and the situation hasn’t improved much.  Mudge talks about the vulnerabilities the L0pht found in highway transponder systems that are still in systems being fielded today.  But more important than the vulnerabilities themselves is the nature of how these vulnerabilities are coming to light.  They are being found by hobbyists, students, and IT people working in their spare time.  How can something as important as the security of public fare collection systems and medical equipment not have a standard process for security acceptance testing? 

As we become more reliant on digital systems, with some even keeping us alive, it is high time for security testing to move beyond student papers and part time IT work.  Security testing needs to become a formal part of the process of purchasing and fielding digital systems.  Our lives are starting to depend on it.