Can’t Trust This!

Last week saw a really interesting bug in TCP come to light. CVE-2016-5696 describes an issue in the way Linux deals with challenge ACKs defined in RFC 5961. The issue itself is really clever and interesting. It’s not exactly new but given the research was presented at USENIX, it suddenly got more attention from the press.

The researchers showed themselves injecting data into a standard http connection, which is easy to understand and terrifying to most people. Generally speaking we operate in a world where TCP connections are mostly trustworthy. It’s not true if you have a “man in the middle”, but with this bug you don’t need a MiTM if you’re using a public network, which is horrifying.
The real story isn’t the flaw though, the flaw is great research and quite clever, but it just highlights something many of us have known for a very long time. You shouldn’t trust the network.

Not so long ago the general thinking was that the public internet wasn’t very trustworthy, but it all worked well enough that things worked. TLS (SSL back then) was created to ensure some level of trust between two endpoints and everything seemed well enough. Most traffic still passed over the network unencrypted though. There were always grumblings about coffee shop attack or nation state style man in the middle, but practically speaking nobody really took these attacks seriously.

The world is different now though. There is no more network perimeter. It’s well accepted that you can’t trust the things inside your network any more than you can trust the things outside your network. Attacks like this are going to keep happening. The network continues to get more complex, which means the number of security problems increases. IPv6 will solve the problem of running out of IP addresses while adding a ton of new security problems in the process. Just wait for the research to start taking a hard look at IPv6.

The joke is “there is no cloud, just someone else’s computer”, there’s also no network, it’s someone else’s network. It’s someone else’s network you can’t trust. You know you can’t trust your own network because it’s grown to a point it’s probably self aware. Now you expect to trust the network of a cloud provider that is doing things a few thousand times more complex than you are? You know all the cloud infrastructures are held together with tape and string too, their networks aren’t magic, they just have really really good paint.

So what’s the point of all this rambling about how we can’t trust any networks? The point is you can’t trust the network. No matter what you’re told, no matter what’s going on. You need to worry about what’s happening on the network. You also need to think about the machines, but that’s a story for another day. The right way to deal with your data is to ask yourself the question “what happens if someone can see this data on the wire?” Not all data is super important, some you don’t have to protect. There is some data you have that must be protected at all times. That’s the stuff you need to figure out how to best do something like endpoint network encryption. If everyone asked this question at least once during development and deployment it would solve a lot of problems I suspect.

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