|21 Jul 2009||#1|
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Office 2010 Application Security
Hello, my name is Brad and I work on the Office security team; we focus on a couple of key areas: building security features that improve the Office product line and driving the security engineering process across the division as part of the Security Development Lifecycle (SDL).
I would like to start with a high-level introduction of several of the new security features in Office 2010, what our goals are, and how we think about them. Because shipping Office isn’t about how we think about it, but instead how you think about it, feel free to ‘send a smile’ with the Technical Preview and let me know if we hit the mark.
Staying ahead of hackers
To start things off, ‘Why?’ is always a good question. Why did we spend time doing anything in this space, and to what end? Well, as the security landscape has been changing, Office has had the misfortune of becoming one of the next big targets for hackers to attack. They have been going after many of our file-format parsers and how we read Office files. They’re looking for ways to exploit bugs and to get their code running on your machine. We have done a lot of work to find and fix bugs, but we can’t find everything. We have to take a more proactive approach and build Office to be more resilient to attack.
To do that, we have designed what we have been referring to as a new security workflow, a layered defense that Office documents have to go through as part of the File Open process. We strive to make this process as invisible as possible. This means no noticeable delay in open times, as well as no dialogs asking you how you feel about security.
File Block improved
The security workflow we designed has several key features that we believe achieves the goals. First, we have improved our File Block feature that was introduced in Office 2007. We now have a way to configure it in the application and have a finer level of granularity to manage how Word, Excel, and PowerPoint open their file types.
Office File Validation: integral and non-intrusive
Another feature is our new binary file-validation system, which call Office File Validation. Since the vast majority of the exploits have focused on our older file formats, pre-dating our XML versions, we built a system that can validate those files to make sure they conform to the documented format, before they are opened by Word, Excel, or PowerPoint. This is something we did in Publisher 2007, which worked out pretty well. Office File Validation is an integral part of Office that on most days, you would never know exists.
The next question is ‘What do you do with those blocked or invalid files?’. Well, if we just blocked a file and said it was invalid, you would probably be pretty curious why it was invalid, or if maybe we made a mistake. Or, you may be sure you know what it is, and still need to read it. Denying you access to these files doesn’t really meet our goals, so we also built another system we call the Protected View.
Protected View: more security, less annoyance
Protected View is a way for us to show Word, Excel, and PowerPoint files to you, but without all of the worry about those files being dangerous. We build up a read-only view of the document in an isolated sandbox, which has minimal access to the system, and no access to your other files and information. Even if the file is malicious, it can’t get out of the sandbox and do harm to your computer or data.
By tying all of these features together into a layered defense, any file that reaches your machine will get inspected for the file format being blocked, tested for validity, and maybe shown in a read-only protected state. All this happens in real time, with an indistinguishable performance impact on your load time, and you can open these Office files without worry.
The other goal to make these features and workflow successful is that they don’t get in the way and instead have a positive impact on your experience. That means fewer dialog boxes and less information that is not actionable. We need to make security smart enough to get out of the way when its job is done. To do that, we have made files that open in Protected View remember when you chose to trust them, so you don’t have to re-trust them next time. You are not less secure; you’re just less annoyed (hopefully!).
In future posts, my team and I will be digging into these and other features to explain how they work and give some insight into how to get the most out of them for system administrators. Stay tuned, and give feedback if you want to hear more about a specific security feature. We hope you enjoy using Office 2010, as much as we have enjoyed working with you toward its creation.
Senior Security PM
Office Trustworthy Computing
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