Monday, June 05, 2017

Some non-lessons from WannaCry

This piece by Bruce Schneier needs debunking. I thought I'd list the things wrong with it.

The NSA 0day debate

Schneier's description of the problem is deceptive:
When the US government discovers a vulnerability in a piece of software, however, it decides between two competing equities. It can keep it secret and use it offensively, to gather foreign intelligence, help execute search warrants, or deliver malware. Or it can alert the software vendor and see that the vulnerability is patched, protecting the country -- and, for that matter, the world -- from similar attacks by foreign governments and cybercriminals. It's an either-or choice.
The government doesn't "discover" vulnerabilities accidentally. Instead, when the NSA has a need for something specific, it acquires the 0day, either through internal research or (more often) buying from independent researchers.

The value of something is what you are willing to pay for it. If the NSA comes across a vulnerability accidentally, then the value to them is nearly zero. Obviously such vulns should be disclosed and fixed. Conversely, if the NSA is willing to pay $1 million to acquire a specific vuln for imminent use against a target, the offensive value is much greater than the fix value.

What Schneier is doing is deliberately confusing the two, combing the policy for accidentally found vulns with deliberately acquired vulns.

The above paragraph should read instead:
When the government discovers a vulnerability accidentally, it then decides to alert the software vendor to get it patched. When the government decides it needs as vuln for a specific offensive use, it acquires one that meets its needs, uses it, and keeps it secret. After spending so much money acquiring an offensive vuln, it would obviously be stupid to change this decision and not use it offensively.

Hoarding vulns

Schneier also says the NSA is "hoarding" vulns. The word has a couple inaccurate connotations.

One connotation is that the NSA is putting them on a heap inside a vault, not using them. The opposite is true: the NSA only acquires vulns it for which it has an active need. It uses pretty much all the vulns it acquires. That can be seen in the ShadowBroker dump, all the vulns listed are extremely useful to attackers, especially ETERNALBLUE. Efficiency is important to the NSA. Your efficiency is your basis for promotion. There are other people who make their careers finding waste in the NSA. If you are hoarding vulns and not using them, you'll quickly get ejected from the NSA.

Another connotation is that the NSA is somehow keeping the vulns away from vendors. That's like saying I'm hoarding naked selfies of myself. Yes, technically I'm keeping them away from you, but it's not like they ever belong to you in the first place. The same is true the NSA. Had it never acquired the ETERNALBLUE 0day, it never would've been researched, never found.


Schneier describes the "Vulnerability Equities Process" or "VEP", a process that is supposed to manage the vulnerabilities the government gets.

There's no evidence the VEP process has ever been used, at least not with 0days acquired by the NSA. The VEP allows exceptions for important vulns, and all the NSA vulns are important, so all are excepted from the process. Since the NSA is in charge of the VEP, of course, this is at the sole discretion of the NSA. Thus, the entire point of the VEP process goes away.

Moreover, it can't work in many cases. The vulns acquired by the NSA often come with clauses that mean they can't be shared.

New classes of vulns

One reason sellers forbid 0days from being shared is because they use new classes of vulnerabilities, such that sharing one 0day will effectively ruin a whole set of vulnerabilities. Schneier poo-poos this because he doesn't see new classes of vulns in the ShadowBroker set.

This is wrong for two reasons. The first is that the ShadowBroker 0days are incomplete. There's no iOS exploits, for example, and we know that iOS is a big target of the NSA.

Secondly, I'm not sure we've sufficiently analyzed the ShadowBroker exploits yet to realize there may be a new class of vuln. It's easy to miss the fact that a single bug we see in the dump may actually be a whole new class of vulnerability. In the past, it's often been the case that a new class was named only after finding many examples.

In any case, Schneier misses the point denying new classes of vulns exist. He should instead use the point to prove the value of disclosure, that instead of playing wack-a-mole fixing bugs one at a time, vendors would be able to fix whole classes of bugs at once.


Schneier cites two studies that looked at how often vulnerabilities get rediscovered. In other words, he's trying to measure the likelihood that some other government will find the bug and use it against us.

These studies are weak, scarcely better than anecdotal evidence. Schneier's own study seems almost unrelated to the problem, and the Rand's study cannot be replicated, as it relies upon private data. Also, there is little differentiation between important bugs (like SMB/MSRPC exploits and full-chain iOS exploits) and lesser bugs.

Whether from the Rand study or from anecdotes, we have good reason to believe that the longer an 0day exists, the less likely it'll be rediscovered. Schneier argues that vulns should only be used for 6 months before being disclosed to a vendor. Anecdotes suggest otherwise, that if it hasn't been rediscovered in the first year, it likely won't ever be.

The Rand study was overwhelmingly clear on the issue that 0days are dramatically more likely to become obsolete than be rediscovered. The latest update to iOS will break an 0day, rather than somebody else rediscovering it. Win10 adoption will break older SMB exploits faster than rediscovery.

In any case, this post is about ETERNALBLUE specifically. What we learned from this specific bug is that it was used for at least 5 year without anybody else rediscovering it (before it was leaked). Chances are good it never would've been rediscovered, just made obsolete by Win10.

Notification is notification

All disclosure has the potential of leading to worms like WannaCry. The Conficker worm of 2008, for example, was written after Microsoft patched the underlying vulnerability.

Thus, had the NSA disclosed the bug in the normal way, chances are good it still would've been used for worming ransomware.

Yes, WannaCry had a head-start because ShadowBrokers published a working exploit, but this doesn't appear to have made a difference. The Blaster worm (the first worm to compromise millions of computers) took roughly the same amount of time to create, and almost no details were made public about the vulnerability, other than the fact it was patched. (I know from personal experience -- we used diff to find what changed in the patch in order to reverse engineer the 0day).

In other words, the damage the NSA is responsible for isn't really the damage that came after it was patched -- that was likely to happen anyway, as it does with normal vuln disclosure. Instead, the only damage the NSA can truly be held responsible for is the damage ahead of time, such as the months (years?) the ShadowBrokers possessed the exploits before they were patched.

Disclosed doesn't mean fixed

One thing we've learned from 30 years of disclosure is that vendors ignore bugs.

We've gotten to the state where a few big companies like Microsoft and Apple will actually fix bugs, but the vast majority of vendors won't. Even Microsoft and Apple have been known to sit on tricky bugs for over a year before fixing them.

And the only reason Microsoft and Apple have gotten to this state is because we, the community, bullied them into it. When we disclose bugs to them, we give them a deadline when we make the bug public, whether or not its been fixed.

The same goes for the NSA. If they quietly disclose bugs to vendors, in general, they won't be fixed unless the NSA also makes the bug public within a certain time frame. Either Schneier has to argue that the NSA should do such public full-disclosures, or argue that disclosures won't always lead to fixes.

Replacement SMB/MSRPC

The ETERNALBLUE vuln is so valuable to the NSA that it's almost certainly seeking a replacement.

Again, I'm trying to debunk the impression Schneier tries to form that somehow the NSA stumbled upon ETERNALBLUE by accident to begin with. The opposite is true: remote exploits for the SMB (port 445) or MSRPC (port 135) services are some of the most valuable vulns, and the NSA will work hard to acquire them.

That it was leaked

The only issue here is that the 0day leaked. If the NSA can't keep it's weaponized toys secret, then maybe it shouldn't have them.

Instead of processing this new piece of information, which is important, Schneier takes this opportunity to just re-hash the old inaccurate and deceptive VEP debate.


Except for a tiny number of people working for the NSA, none of us really know what's going on with 0days inside government. Schneier's comments seem more off-base than most. Like all activists, he deliberately uses language to deceive rather than explain (like "discover" instead of "acquire"). Like all activists, he seems obsessed with the VEP, even though as far as anybody can tell, it's not used for NSA acquired vulns. He deliberate ignores things he should be an expert in, such as how all patches/disclosures sometimes lead to worms/exploits, and how not all disclosure leads to fixes.


darkfader said...

The same is true the NSA. Had it never acquired the ETERNALBLUE 0day, it never would've existed in the first place.

I don't know how that is ever supposed to be true.

amantes said...

When you find a security bug you aren't creating a vulnerability. It already existed.

Unless you are suggesting the NSA paid someone that went back in time, managed to get employed by Microsoft, and introduced bugs in SMB code.

Daniel Sutherland said...

The value of something isn't what you're willing to pay for it (that's the cost), it's the utility it provides. A vuln that is incidentally found can still be of great value even if the cost was minimal, and therefore an argument can be made not to disclose it.

Also the damage of ETERNALBLUE is not limited to WannaCry + variants, it's that plus whatever other quieter uses have been found for it prior to SB disclosure/ MS patching, which could be significant.

Chris Schmidt said...

Rob, while I agree wholeheartedly that Bruce made quite a few assumptions and did in fact misstate things in the post; I think that you're also making some pretty significant assumptions. For instance, assuming that the US is the only actor that knew about and/or was actively exploiting ETERNALBLUE is probably the biggest and most apparent. I find it naive (generally) to assume that if ETERNALBLUE was acquired, as you proclaim - that the "arms dealer" they acquired it from simply stopped anyone else from purchasing or "acquiring" the same 0-day. Rediscovery probability aside, an arms dealer is interested in money. If the exploit (and if it was acquired, let's be honest - it was weaponized for them, as part of the deal) was actually discovered through internal research that changes the dynamics only slightly. As you yourself state, the studies on rediscoverability are misleading (to put it mildly) and assume that only those who disclose that they've discovered a vuln are capable of discovering them. We simply don't know, nor is it likely that we ever will, to what extent the ETERNALBLUE *exploit* was being used prior to disclosure.

At this point, it's all conjecture and speculation, from both Bruce and yourself on the matter. I think that this post is equally as irresponsible as Bruce's as a highly visible member of the infosec community with little to no actual material to back up what's being said. I respect that your intent was to call out curmudgeonly behavior by Bruce but it feels like you fell directly into the same trap.

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