On backdoors and malicious code

So since the ASVS 3.0 retired much of the malicious code requirements, and after actually doing a line by line search of ~20 kLOC of dense J2EE authentication code, I’ve been thinking about various methods that backdoors might be created and not be findable by both automated and line by line searches.

This obviously has an issue with the recent Juniper revelation that they found a backdoor in the VPN code of their SOHO device firmware. It also feels like the sort of thing that Apple suffered with GOTO FAIL, and Linux suffered a long time ago with the wait4 backdoor.


So basically, I’ve been thinking that there obviously has to be a group dedicated to obfuscated backdooring. Making code that passes the visual and automated muster of specialists like me. There is probably another group or portion of the same group that sets about gaining sufficient privileges to make these changes without being noticed.

So before anyone goes badBIOS on me, I think it would be useful if we started to learn what malicious coding looks like in every language likely to be backdoored.

We can help prevent these attacks by improving the agile SDLC process, and keeping closer tabs on our repos. We can also make it more difficult to slip these things in if folks stuck to an agreed formatting style that made slipping in these types of attacks much harder, primarily by using automated indentation and linting that detected the lack of block control and assignment during conditionals. Yes, this will make some code visually longer, but we cannot tolerate more backdoors.

I’ve been doing a LOT of agile SDLC security work in the last few years, working WITH the developers on creating actually secure development processes and resilient applications, rather than reviewing the finished product and declaring their babies ugly. The latter does not work. You cannot review your way to building secure applications. We need to work with developers.

This is important as we’re starting to see an explosion in language use. It’s not merely enough to understand how these things are done in C or C++, but any system language, and any up and coming languages, many of whom we have zilch, nada, nothing in the way of automated tools, code quality tools, and specialists familiar with Go, Clojure, Haskell, and any number of other languages I see pop up from time to time.

What I think doesn’t work is line by line reviewing. All of these pieces of code must be have been looked at by many people (the many eyeballs fallacy) and run past a bunch of automated source code analysis tools, and it was “all good”, but it wasn’t really. Who knows how many secure code review specialists like me looked at the code? We need better knowledge and better techniques that development shops can implement. I bet we haven’t seen the last of Juniper style attacks pop up. Most firms are yet to really look through their unloved bastard repos full of code from developers past, present and future.

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