You’ve just approved an audit of your codebase. Do you:
- Send a copy of the repository and wait for the auditors’ reports, or
- Take the extra effort to set the auditors up for success?
By the end of the audit, the difference between these answers will lead to profoundly disparate results. In the former case, you’ll waste money, lose time, and miss security issues. In the latter case, you’ll reduce your risk, protect your time, and get more valuable security guidance.
It’s an easy choice, right?
Glad you agree.
Now, here’s how to make that audit more effective, valuable, and satisfying for everybody involved.
Set a goal for the audit
This is the most important step of an audit, and paradoxically the one most often overlooked. You should have an idea of what kind of question you want answered, such as:
- What’s the overall level of security for this product?
- Are all client data transactions handled securely?
- Can a user leak information about another user?
Knowing your biggest area of concern will help the auditing team tailor their approach to meet your needs.
Resolve the easy issues
Handing the code off to the auditing team is a lot like releasing the product: the cleaner the code, the better everything will go. To that end:
- Enable and address compiler warnings. Go after the easy stuff first: turn on every single compiler warning you can find, understand each warning, then fix your code until they’re all gone. Upgrade your compiler to the latest version, then fix all the new warnings and errors. Even innocuous seeming warnings can indicate problems lying in wait.
- Increase unit and feature test coverage. Ideally this has been part of the development process, but everyone slips up, tests don’t get updated, or new features don’t quite match the old integrations tests. Now is the time to update the tests and run them all.
- Remove dead code, stale branches, unused libraries, and other extraneous weight. You may know which branch is active and which is dead but the auditors won’t and will waste time investigating it for potential issues. The same goes for that new feature that hasn’t seen progress in months, or that third-party library that doesn’t get used anymore.
Some issues will persist — a patch that isn’t quite ready, or a refactor that’s not integrated yet. Document any incomplete changes as thoroughly as possible, so that your auditors don’t waste a week digging into code that will be gone in two months’ time.
Document, Document, Document
Think of an audit team as a newly hired, fully remote developer; skilled at what they do, but unfamiliar with your product and code base. The more documentation, the faster they’ll get up to speed and the sooner they’ll be able to start their analysis.
- Describe what your product does, who uses it, and how. The most important documentation is high level: what does your product do? What do users want from it? How does it achieve that goal? Use clear language to describe how systems interact and the rationale for design decisions made during development.
- Add comments in-line with the code. Functions should have comments containing high-level descriptions of their intended behavior. Complicated sections of code should have comments describing what is happening and why this particular approach was chosen.
- Label and describe your tests. More complicated tests should describe the exact behavior they’re testing. The expected results of tests, both positive and negative, should be documented.
Include past reviews and bugs. Previous audit reports can provide guidance to the new audit team. Similarly, documentation regarding past security-relevant bugs can give an audit team clues about where to look most carefully.
Deliver the code batteries included
Just like a new fully remote developer, the audit team will need a copy of the code and clear guidance on how to build and deploy your application.
- Prepare the build environment. Document the steps to create a build environment from scratch on a computer that is fully disconnected from your internal network. Where relevant, be specific about software versions. Walk through this process on your own to ensure that it is complete. If you have external dependencies that are not publicly available, include them with your code. Fully provisioned virtual machine images are a great way to deliver a working build environment.
- Document the build process. Include both the debug and release build processes, and also include steps on how to build and run the tests. If the test environment is distinct from the build environment, include steps on how to create the test environment. A well-documented build process enables an auditor to run static analysis tools far more efficiently and effectively.
- Document the deploy process. This includes how to build the deployment environment. It is very important to list all the specific versions of external tools and libraries for this process, as the deployment environment is a considerable factor in evaluating the security of your product. A well-documented deployment process enables an auditor to run dynamic analysis tools in a real world environment.
At this point you’ve handed off your code, documentation, and build environment to the auditors. All that prep work will pay off. Rather than puzzling over how to build your code or what it does, the audit team can immediately start work integrating advanced analysis tools, writing custom fuzzers, or bringing custom internal tools to bear. Knowing your specific goals will help them focus where you want them to.
An audit can produce a lot of insight into the security of your product. Having a clear goal for the audit, a clean codebase, and complete documentation will not only help the audit, it’ll make you more confident about the quality of the results.
Interested in getting an audit? Contact us to find out what we can do for you.
Resolve the easy issues
- Enable and address every last compiler warning.
- Increase unit and feature test coverage.
- Remove dead code, stale branches, unused libraries, and other extraneous weight.
- Describe what your product does, who uses it, why, and how it delivers.
- Add comments about intended behavior in-line with the code.
- Label and describe your tests and results, both positive and negative.
- Include past reviews and bugs.
Deliver the code batteries included
- Document the steps to create a build environment from scratch on a computer that is fully disconnected from your internal network. Include external dependencies.
- Document the build process, including debugging and the test environment.
- Document the deploy process and environment, including all the specific versions of external tools and libraries for this process.
*** This is a Security Bloggers Network syndicated blog from Trail of Bits Blog authored by garretreece. Read the original post at: https://blog.trailofbits.com/2018/04/06/how-to-prepare-for-a-security-audit/