The Security Patch Dilemma For Scripting And VM Based Languages

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In his book, Producing Open Source Software, Karl Fogel gives sage advice on running an open source project. The section on how to deal with a security vulnerability was particularly interesting to me last night.

Upon learning of a potential security hole, Karl recommends the following:

  1. Don’t talk about the bug publicly until a fix is available.
  2. Make sure to have a private mailing list setup with a small group of trusted committers where users can send security reports.
  3. Fix the patch quickly. Time is of the essence.
  4. Don’t commit the fix into your source control lest someone scanning for such vulnerabilities find out about it. Wait till after the fix is released.
  5. Give well known administrators (and thus likely targets) using the software a heads up before announcing the flaw and the fix.
  6. Distribute the fix publicly.

There’s more elaboration in the book, but I think the above list distills the key points. Karl’s advice is born from his experience working on CVS and leading the Subversion project and makes a lot of sense.

But for a project built on Java, .NET, or a scripting language, there is an interesting dilemma. The security fix itself announces the vulnerability.

When the Subversion team releases a patch, it is generally compiled to native machine code, which is effectively opaque to the world. Sure with time and effort, a native executable can be decompiled, but the barrier is high to discover the actual exploit by examining the binary. It buys consumers time to patch their installations before exploits start becoming rampant.

With a language like C#, Java, or Ruby, the bar to looking at the code is extremely low. Such languages can raise the bar slightly by using obfuscators, but that is really not common for an Open Source project and creates very little delay for the determined attacker.

So no matter how well you keep the flaw private until you’re ready to announce the fix. The announcement and publication of the fix itself potentially points attackers to the flaw.

This is one situation in which the increased transparency of such languages can cause a problem. Consumers of projects built on these languages have to be extra vigilant about applying patches quickly, while developers of such code must be extra vigilant in threat modeling and code review to avoid security vulnerabilities in the first case. Then again, this doesn’t mean that code compiled to a native binary should be any less vigilant about security.\

If you have a better way of distributing security patches for VM-based/Scripting language projects than this, please do tell.

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