Thursday, October 08, 2009

The .NET Developer’s Guide to Windows Security

image A month ago I started a new reading regime where I get up an hour earlier and head off to a café for an hour’s reading before work. It’s a very nice arrangement, since I seem to be in the perfect state of mind for a bit of technical reading first thing in the morning, and an hour is just about the right length of time to absorb stuff before my brain starts to hit overload.

I’ve had this book sitting on my bookshelf unread for a year or two, so it was the perfect candidate to kick off the new regime.

The book is formatted as a list of 75 items such as; “How to Run a Program as Another User”, “What is Role-Based Security”, “How to Use Service Principle Names”. The author, Keith Brown, has an easy to read style that dispatches answers clearly and expertly. Like all the best technical books, he doesn’t just say how things work, but often includes a little history about why they work that way. He’s also quick to outline best practices and share his opinion about the best security choices.

I think most Windows developers, me included, have a cargo-cult view of Windows Security. We pick up various tips and half-truths over the years and get around most security issues by a process of trial and error. All too often we simply give our applications elevated permissions simply because that’s the only way we can get them to work. A book like this should be essential reading, but unfortunately security is often some way down our list of priorities.

Keith Browns first and often repeated message is that we should always develop as a standard user. I’ve been doing this at home for some years now; in fact my first ever post on this blog back in 2005 was on this very subject. However, I can’t think of a single assignment I’ve had where my client’s developers where not logged in as Administrator. What little I do know about security has come from my standard user development experience, it makes you fully aware of what privileges your software is demanding and I’ve found I’ve been bitten far less by security related bugs. Working as a standard user is a message that’s drummed home throughout the book and is probably the best advice you could take away from it.

I’ve also gained a real insight into the way logon sessions work and how security tokens attach to them. I had no idea that every Windows resource has an owner and the implications of ownership. The sections on Kerberos, delegation and impersonation were also real eye-openers.

So if you too have misty ideas about how security works, you owe to yourself to read this book. Sure it’s not a very sexy subject, but it’ll make you a far better developer.

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