The Insecurity of Ambiguous Standards
Why are networks so insecure?
One reason is we don’t take network security seriously. We just don’t think of the network as a serious target of attack. Or we think of security as a problem “over there,” something that exists in the application realm, that needs to be solved by application developers. Or we think the consequences of a network security breach as “well, they can DDoS us, and then we can figure out how to move load around, so if we build with resilience (enough redundancy) we’re already taking care of our security issues.” Or we put our trust in the firewall, which sits there like some magic box solving all our problems.
The problem is–none of this is true. In any system where overall security is important, defense-in-depth is the key to building a secure system. No single part of the system bears the “primary responsibility” for “security.” The network is certainly a part of any defense-in-depth scheme that is going to work.
Which means network protocols need to be secure, at least in some sense, as well. I don’t mean “secure” in the sense of privacy—routes are not (generally) personally identifiable information (there are always exceptions, however). But rather “secure” in the sense that they cannot be easily attacked. On-the-wire encryption should prevent anyone from reading the contents of the packet or stream all the time. Network devices like routers and switches should be difficult to break in too, which means the protocols they run must be “secure” in the fuzzing sense—there should be no unexpected outputs because you’ve received an unexpected input.
I definitely do not mean path security of any sort. Making certain a packet (or update or whatever else) has followed a specified path is a chimera in packet switched networks. It’s like trying to nail your choice of multicolored gelatin desert to the wall. Packet switched networks are designed to adapt to changes in the network by rerouting traffic. Get over it.
So why are protocols and network devices so insecure? I recently ran into an interesting piece of research that provides some of the answer. To wit—
Our research saw that ambiguous keywords SHOULD and MAY had the second highest number of occurrences across all RFCs. We’ve also seen that their intended meaning is only to be interpreted as such when written in uppercase (whereas often they are written in lowercase). In addition, around 40% of RFCs made no use of uppercase requirements level keywords. These observations point to inconsistency in use of these keywords, and possibly misunderstanding about their importance in a security context. We saw that RFCs relating to Session Initiation Protocol (SIP) made most use of ambiguous keywords, and had the most number of implementation flaws as seen across SIP-based CVEs. While not conclusive, this suggests that there may be some correlation between the level of ambiguity in RFCs and subsequent implementation security flaws.
In other words, ambiguous language leads to ambiguous implementations which leads to security flaws in protocols.
The solution for this situation might be just this—specify protocols more rigorously. But simple solutions rarely admit reality within their scope. It’s easy to build more precise specifications—so why aren’t our specifications more precise?
In a word: politics.
For every RFC I’ve been involved in drafting, reviewing, or otherwise getting through the IETF, there are two reasons for each MAY or SHOULD therein. The first is someone has thought of a use-case where an implementor or operator might want to do something that would be otherwise not allowed by MUST. In these cases, everyone looks at the proposed MAY or SHOULD, thinks about how not doing it might be useful, and then thinks … “this isn’t so bad, the available functionality is a good thing, and there’s no real problem I can see with making this a MAY or SHOULD.” In other words, we can think of possible worlds where someone might want to do something, so we allow them to do it. Call this the “freedom principle.”
The second reason is that multiple vendors have multiple customers who want to do things different ways. When the two vendors clash in the realm of standards, the result is often a set of interlocking MAYs and SHOULDs that allow two implementors to build solutions that are interoperable in the main, but not along the edges, that satisfy both of their existing customer’s requirements. Call this the “big check principle.”
The problem with these situations is—the specification has an undetermined set of MAYs and SHOULDs that might interlock in unforeseen ways, resulting in unanticipated variances in implementations that ultimately show up as security holes.
Okay—now that I’ve described the problem, what can you do about it? One thing is to simplify. Stop putting everything into a small set of protocols. The more functionality you pour into a protocol or system, the harder it is to secure. Complexity is the enemy of security (and privacy!).
As for the political problems, these are human-scale, which means they are larger than any network you can ever build—but I’ll ponder this more and get back to you if I come up with any answers.