Thursday, March 7, 2013

Peer reviews for security are a waste of time?

At this year’s RSA conference, one of the panel’s questioned whether software security is a waste of time. A panellist, John Viega, said a few things that I agreed with, and a lot that I didn't. Especially that

“peer reviews for security are a waste of time.”

This statement is wrong on every level.

Everyone should know by now that code reviews find real bugs – even informal, lightweight code reviews.

“Reviews catch more than half of a product’s defects regardless of the domain, level of maturity of the organization, or lifecycle phase during which they were applied”. What We Have Learned About Fighting Defects

Software security vulnerabilities are like other software bugs – you find them through testing or through reviews. If peer code reviews are a good way to find bugs, why would they be a waste of time for finding security bugs?

There are only a few developers anywhere who write security plumbing: authentication and session management, access control, password management, crypto and secrets handling. Or other kinds of plumbing like the data access layer and data encoding and validators that also have security consequences. All of this is the kind of kind of stuff that should be handled in frameworks anyway – if you’re writing this kind of code, you better have a good reason for doing it and you better know what you are doing. It’s obviously tricky and high-risk high-wire work, so unless you’re a team of one, your code and decisions need to be carefully reviewed by somebody else who is at least as smart as you are. If you don’t have anyone on the team who can review your work, then what the hell are you doing trying to write it in the first place?

Everybody else has to be responsible for writing good, defensive application code. Their responsibilities are:

  • Make sure their code works – that the logic is correct
  • Use the framework properly
  • Check input data and return values
  • Handle errors and exceptions correctly
  • Use safe routines/APIs/libraries
  • Be careful with threading and locking and synchronization

A good developer can review this code for security and privacy requirements: making sure that you are masking or encrypting or – even better – not storing PII and secrets, auditing, properly following access control rules. And they can review the logic and workflow, look for race conditions, check data validation, make sure that error handling and exception handling is done right and that you are using frameworks and libraries carefully.

This is what code reviews are for. To look for and find coding problems. If you find these problems – and code reviews are one of the most effective ways of doing this – your code will be safer and more secure. So I don’t get it. Why are peer reviews for security a waste of time?

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