Category Archives: Books

Security Research Is Threat Modeling’s Constructive Criticism

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(the following is partially excerpted from my next book)

Adam Shostack, author of Threat Modeling: Designing for Security has succinctly described a process of constructive critique within engineering:

“The back and forth of design and critique is not only a critical part of how an individual design gets better, but fields in which such criticism is the norm advance faster.”

The Spectre/Meltdown issues are the result of a design critique such as Shostack describes in his pithy quote given above.  In fact, one of the fundamental functions that I believe security research can play is providing designers with a constructive critique.

Using Spectre and Meltdown as an example of engineering critique, let’s look at some of the headlines from before the official issue announcement by the researchers:

“Kernel-memory-leaking Intel processor design flaw forces Linux, Windows redesign”, John Leyden and Chris Williams 2 Jan 2018 at 19:29, The Register, https://www.theregister.co.uk/2018/01/02/intel_cpu_design_flaw/

“A CRITICAL INTEL FLAW BREAKS BASIC SECURITY FOR MOST COMPUTERS”, Andy Greenberg, January 3, 2018, Wired Magazine, https://www.wired.com/story/critical-intel-flaw-breaks-basic-security-for-most-computers/

There were dozens of similar headlines (many merely repeating the first few, especially, The Register’s), all declaiming a “flaw” in CPUs. I want to draw the reader’s attention to the word, “flaw”. Are these issues “flaws”? Or, are they the result of something else?

The Register headline and that first article were based upon speculation that had been occurring amongst the open source community supporting the Linux Kernel. A couple of apparently odd changes that had been made to kernel code. But, the issues to which these changes responded were “embargoed”, that is, the reasoning behind the changes was known only to those making the changes.

Unlike typical open source changes, whose reasoning is public and often discussed by members of the community, these kernel changes had been made in opaquely without public comment, which of course, set concerned kernel community members wondering.

To observers not familiar with the reasoning behind the changes, it was clear that something was amiss and likely in relation to CPU functions; anxious observers were guessing what might be the motivation for those code changes.

Within the digital security universe, there exists an important dialog between security research aimed at discovering new attack techniques and the designers of the systems and protocols upon which that research is carried out. As Adam noted so very wryly, achieving solid designs, even great ones, and most importantly, resilient designs in the face of omnipresent attack requires an interchange of constructive critique. That is how Spectre and Meltdown were discovered and presented.

Neither of this collection of (at the time of announcement) new techniques involved exercising a flaw, that is, a design error – in other words, the headlines quoted just above were erroneous and rather misleading[2].

Speculative execution and the use of kernel mapped user memory pages by operating systems were intentional design choices that had been working as designed for more than 10 years. Taken together, at least some of the increases in CPU performance over that period can directly be tied to speculative execution design.

Furthermore, and quite importantly to this discussion, these design choices were made within the context of a rather different threat landscape. Some of today’s very active threat actors didn’t exist, or at least, were not nearly as active and certainly not as technically sophisticated circa 2005 as they are today, May 2018.

If I recall correctly (and I should be able to remember, since I was the technical lead for Cisco’s Web infrastructure and application security team at that time), in 2005, network attacks were being eclipsed by application focused attack methods, especially, web attack methods.

Today, web attacks are very “ho, hum”, very run of the ordinary, garden variety. But in 2005, when the first CPU speculative execution pipelines were being released, web applications were targets of choice at the cutting edge of digital security. Endpoint worms and gaining entrance through poor network ingress controls had been security’s focus up until the web application attack boom (if I may title it so?). At about that time, targeting web applications was fast displacing network periphery concerns. Attackers were in the process of shifting to targets that used a standard protocol (HTTP) which was guaranteed to pass through organizational firewalls. Many of the new targets’ were becoming always  available via the Public Internet.

Since the web application attack boom, attacks and targets have continued to evolve. The threat landscape changed dramatically over the years since the initial design of speculative execution CPUs. Alongside the changes in types of attackers as well as their targets, attacker and researcher sophistication has grown, as has an attackers’ toolbox. 2018 is a different security world than 2005. I see no end to this curve of technical growth in my crystal ball.

The problem is, when threat modeling, whether in 2005 or 2018, one considers the attacks of the past, those of moment, and then one must try one’s best to project from current understanding to attacks that might arise within the foreseeable future. Ten or twelve years seems an awfully long horizon of prescience, especially when considering the rate at which technical change continues to take place.

As new research begins to chew at the edges of any design, I believe that the wise and diligent practitioner revisits their existing threat models in light of developments.

If I were to fault the CPU and operating system makers whose products are subject to Spectre or Meltdown, it would be for a failure to anticipate where research might lead, as research has unfolded. CPU threat modelers could have taken into account advances in research indicating unexpected uses of cache memory.

Speculative execution leaves remnants of a speculated execution branch in cache memory when a branch has not been taken. It is those remnants that lie at the heart of this line of research.

A close examination of the unfolding research might very well have led those responsible for updating CPU threat models to consider the potential for something like Spectre and Meltdown. (Or, perhaps the threat models were updated, but other challenges prevented updates to CPU designs? CPU threat modelers, please tell us all what the real story is)

I’ve found a publication chain during the 3 years previous that, to me, points towards the new techniques. Spectre and Meltdown are not stand-alone discoveries, but lie on a body of CPU research that had been published regularly for several years.

As I wrote for McAfee’s Security Matters blog in January of 2018 (as a member of McAfee’s Advanced Threat Research Team),

“Meltdown and Spectre are new techniques that build upon previous work, such as “KASLR”  and other papers that discuss practical side-channel attacks. The current disclosures build upon such side-channels attacks through the innovative use of speculative execution….An earlier example of side-channel based upon memory caches was posted to Github in 2016 by one of the Spectre/Meltdown researchers, Daniel Gruss.” Daniel Gruss is one of the Spectre and Meltdown paper authors.

Reading these earlier papers, it appears to me that some of the parent techniques that would be used for the Spectre and Meltdown breakthroughs could have been read (should have been read?) by CPU security architects in order to re-evaluate the CPU’s threat model. That previously published research was most certainly available.

Of course, hindsight is always 20/20; I had the Spectre and Meltdown papers in hand as I reviewed previous research. Going the other way might be more difficult?

Spectre and Meltdown did not just spring miraculously from the head of Zeus, as it were. They are the results of a fairly long and concerted effort to discover problems with and thus, hopefully, improve the designs of modern processors. Indeed, the researchers engaged in responsible disclosure, not wishing to publish until fixes could be made available.

To complete our story, the driver that tipped the researchers to an early, zero-day disclosure (that is, disclosure without available mitigations or repairs) were the numerous speculative (if you’ve forgive the pun?) journalism (headlines quoted above) that gained traction based upon misleading (at best) or wrong conclusions. Claiming a major design “flaw” in millions of processors is certainly a reader catching headline. But, unfortunately, these claims were vastly off the mark since no flaw existed in the CPU or operating system designs.

While it may be more “interesting” to imagine a multi-year conspiracy to cover up known design issues by evil CPU makers, no such conspiracy appears to have taken place.

Rather, in the spirit of responsible disclosure, the researchers were waiting for mitigations to be made available to customers; CPU manufacturers and operating system coders were heads down at work figuring out what appropriate mitigations might be, and just how to implement these with the least amount of disruption. None of these parties was publicly discussing just why changes were being made, especially to the open source Linux kernel.

Which is precisely what one would expect in order to protect millions of CPU users: embargo the technical details to foil attackers. There is actually nothing unusual about such a process; it’s all very normal and typical, and unfortunately for news media, quite banal[3].

What we see through the foregoing example about Spectre and Meltdown is precisely the sort of rich dialog that should occur between designers and critics (researchers, in this case).

Designs are built against the backdrop and within the context of their security “moment”. Our designs cannot improve without collective critique amongst the designers; such dialog internal to an organization or at least, a development team is essential. I have spoken about this process repeatedly at conferences: “It takes a village to threat model,” (to misquote a famous USA politician.)

But, there’s another level, if you will, that can reach for a greater constructive critique.

Once a design is made available to independent critics, that is, security researchers, research discoveries can and I believe, should become part of an ongoing re-evaluation of the threat model, that is, the security of the design. In this way, we can, as an industry, reach for the constructive critique called for by Adam Shostack.

[1]In my humble experience, Adam is particularly good at expressing complex processes briefly and clearly. One of his many gifts as a technologist and leader in the security architecture space.

[2]Though salacious headlines apparently increase readership and thus advertising revenue. Hence, the misleading but emotion plucking headlines.

[3]Disclosure: I’ve been involved in numerous embargoed issues over the years.

“We sell Hammers” – Not Security!

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“We sell Hammers” – Not Security!

“Several former Home Depot employees said they were not surprised the company had been hacked. They said that over the years, when they sought new software and training, managers came back with the same response: “We sell hammers.””

Failure to understand the dependence that we have not just on our obvious digital devices – smart phone, laptop, tablet, fancy fitness bling on your wrist – but also on a matrix of interconnection tying all these devices and billions more together – will land you in the hot seat. For about three billion out of the seven billion people on this planet, we have long since passed the point where we are isolated entities who act alone and in some measure of unconnected global anonymity. For most of us, our lives are not just dependent upon technology itself, but also on the capabilities of innumerable, faceless business entities acting on our behalf.

Consider the following, common, but trivial example.

When I swipe my credit card at the pump to purchase petrol, that transaction passes through any number of computation devices and applications operated by a chain of business entities. The following is a typical scenario (an example flow – but not the only one, of course):

  • The point of sale device1, itself (likely supplied by a point of sale provider)
  • The networking equipment at the station2
  • The station’s Internet provider’s equipment (networking, security, applications – you have no idea!)
  • One or more telecom company’s networking infrastructure across the Internet backbone
  • The point of sale company or their proxy
  • More networking equipment and Internet providers
  • A credit card payment processor
  • More networking equipment and Internet providers
  • The card issuer who must validate the card and agree to pay the transaction for me

And so on…. All just to fill my tank up. It’s seamless and invisible – the communications between entities usually bring up an encrypted tunnel, though the protection offered is not as solid as you may hope – Invisible and seamless, except when the processing is not so invisible, like during a compromise and breach.

Every one of these invisible players has to have good enough security to protect me, and you, if you also use some sort of payment card for your petrol.

Home Depot, and Target before them, (and who knows who’s next?) failed to understand that in order to sell a hammer in the Internet world, you’re participating in this huge web of digital interconnection. Even more so, if you’re large enough, your business network will have become an eco-system of digital entities, many of whose security practices will affect your security posture in fairly profound ways. When 2 (or more) systems connect, each may affect the security posture of the other, sometimes in profound ways.

And there be pirates in them waters, Matey. As I wrote in the introduction to my next book, Securing Systems: Applied security architecture and threat models:

“…as of this writing, we are engaged in a cyber arms race of extraordinary size, composition, complexity, and velocity.”

One of the biggest problems for security practitioners remains that the cyber “arms race” isn’t just between a couple of nation-states. Foremost, the nation-state cyber war has to cross the same digital ocean that we use for our daily lives and digital entertainment. The shared web makes every digital citizen, potential “collateral damage”. But, there are more players than governments.

As can occur in a ground war, virtual “warlords” have private cyber armies marauding for loot, my loot, your loot. Those phishing spam don’t come from your friends, right3? Just trying to categorize the various entities engaged in cyber attacks could generate a couple of fine PhD theses and perhaps even provide years of follow-on papers? The number and varying loyalties of the many players who carry out cyber attacks increases the “size” of the problem, adds to the “composition”, and generates a great deal of “complexity”. It’s enough to make a well-meaning box-store retailer bury its collective head in the virtual sand. Which is precisely what happened to that hammer seller, Home Depot.

But answering the “who” doesn’t complete the picture. There’s the macro “how”, as well4. The Internet seems to suffer the “tragedy of the commons“.

In order to keep the Internet sufficiently interesting with compelling content such that we want to participate, it absolutely must remain neutral in character5. While Internet democracy certainly appears to be quite messy, the very thing that drives the diversity of content on the Internet is its level playing field6.

But leaving the Internet as an open field for all to enjoy means that some will take advantage of the many simply because the “pickings” are too rich to ignore. There is just too much to steal to let those resources lay untouched. And the pirates don’t! People actually do answer those “Nigerian Prince” scam emails. Really, someone does. People do buy those knock-off drugs. For the 3 billion of us who are digitally connected, it’s a dangerous digital day, every single day. Watch what you click!

In short, if you’re reading this on my blog site, you are perhaps an unwitting participant in that “cyber arms race of extraordinary size, composition, complexity, and velocity.” And so is every business that employs modern digital capabilities, whether for payments, or any other task. Failure to understand just how dependent a business is upon this matrix of digital interaction will make one a Target (pun intended). CEO’s, you may want to pay closer attention? Ignoring the current realities could cost you your job, perhaps even your career7!

If you think that you only sell objects and not some level of digital security, I fear that you are likely to be very sadly mistaken?

cheers,

/brook

  1. My friend and former colleague, Lucy McCoy, wrote the communications code in the first generation of gas pump payment terminals. At that time, terminals communicated via modem and phone line. She was a serial communications wiz. I remember the point of sale terminal laid out in her lab area. Lucy has since passed away. She was a brilliant engineer; she gave my code the best quality testing ever.
  2. The transactions have to get from station to payment processing, right? Who runs those cable modems and routers at the station? Could be the Internet provider, or maybe not. I run my own modem/routers/switches at home to which I have full admin access.
  3. I don’t know any spammers, as far as I know? Perhaps I make an unwarranted assumption that you don’t, either?
  4. The “what” and “why” of cyber attack seem pretty clear. Beyond attackers after money, they are after some other advantage: geo-political, business, just causes (pick your favourite or most hated cause), career enhancement, what-have-you. This is all pretty well documented. The security industry seems preoccupied with the “what”, i.e., the technical details of exploits. Again, these technical details seem pretty well documented.
  5. Imagine if your most hated or feared government had control over your Internet use, even the Internet itself, and proceeded to feed you exactly what they wanted you to know and prevented you from any other content. How would you like that?
  6. The richness and depth that is an emergent and continuing quality of the Internet, to me, demonstrates the absolute genius of the originators and early framers of the protocols and design.
  7. Of course, if I had a severance of $15.9 million, maybe I wouldn’t very much mind ending my career?

Book Signing At RSA

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I’m signing books along with James Ransome and Anmol Misra at 11:30AM at the bookstore at RSA in San Francisco, Digital Guru. If you’re at the conference, please do come by and say “hello”.

James and Anmol  were kind enough to give me a few of their book’s pages, Core Software Security, so that I could ramble on about Secure Development Lifecycles (SDL).

cheers,

/brook

The “Real World” of Developer-centric Security

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My friend and colleague, Dr. James Ransome, invited me late last Winter to write a chapter for his 10th book on computer security, Core Software Security, (with co-author, Anmol Misra)  published by CRC Press. My chapter is “The SDL In The Real World”, SDL = “Secure Development Lifecycle”. The book was released December 9, 2013. You can get copies from the usual sources (no adverts here, as always).

It was an exciting process. James and I spent hours white boarding possible SDL approaches, which was very fun, indeed*. We collectively challenged ourselves to uncover current SDL assumptions, poke at the validity of these, and find better approaches, if possible.

Many of you already know that I’ve been working towards a different approach to the very difficult, multi-dimensional and multi-variate problem of designing and implementing secure software for a rather long time. Some of my earlier work has been presented to the industry on a regular basis.

Specifically, during the period of 2007-9, I talked about a new (then) approach to security verification that would be easy for developers to integrate into their workflow and which wouldn’t require a deep understanding of security vulnerabilities nor of security testing. At the time, this approach was a radical departure.

The proving ground for these ideas was my program at Cisco, Baseline Application Vulnerability Assessment, or BAVA, for short (“my” here does not exclude the many people who contributed greatly to BAVA’s structure and success. But it was more or less my idea and I was the technical leader for the program).

But, is ease and simplicity all that’s necessary? By now, many vendors have jumped on the bandwagon; BAVA’s tenets are hardly even newsworthy at this point**. Still, the dream has not been realized, as far as I can see. Vulnerability scanning still suffers from a slew of impediments from a developer’s view:

  • Results count vulnerabilities not software errors
  • Results are noisy, often many variations of a single error are reported uniquely
  • Tools are hard to set up
  • Tools require considerable tool  knowledge and experience, too much for developers’ highly over-subscribed days
  • Qualification of results requires more in-depth security knowledge than even senior developers generally have (much less an average developer)

And that’s just the tool side of the problem. What about architecture and design? What about building security in during iterative, fast paced, and fast changing agile development practices? How about continuous integration?

As I was writing my chapter, something crystalized. I named it, “developer-centric security”, which then managed to get wrapped into the press release and marketing materials of the book. Think about this:  how does the security picture change if we re-shape what we do by taking the developer’s perspective rather than a security person’s?

Developer-centric software security then reduced to single, pointed question:

What am I doing to enable developers to innovate securely while they are designing and writing software?

Software development remains a creative and innovative activity. But so often, we on the security side try to put the brakes on innovation in favour of security. Policies, standards, etc., all try to set out the rules by which software should be produced. From an innovator’s view at least some of the time, developers are iterating through solutions to a new problem while searching for the best way to solve it. How might security folk enable that process? That’s the question I started to ask myself.

Enabling creativity, thinking like a developer, while integrating into her or his workflow is the essence of developer-centric security. Trust and verify. (I think we have to get rid of that old “but”)

Like all published works, the book represents a point-in-time. My thinking has accelerated since the chapter was completed. Write me if you’re intrigued, if you’d like more about developer-centric security.

Have a great day wherever you happen to be on this spinning orb we call home, Earth.

cheers,

/brook

*Several of the intermediate diagrams boggle in complexity and their busy quality. Like much software development, we had to work iteratively. Intermediate ideas grew and shifted as we worked. a creative process?

**At the time, after hearing BAVA’s requirements, one vendor told me, “I’ll call you back next year.”. Six months later on a vendor webcast, that same vendor was extolling the very tenets that I’d given them earlier. Sea change?