.net - Memory randomization as application security enhancement?

Question

I recently came upon a Microsoft article that touted new "defensive enhancements" of Windows 7. Specifically:

• Address space layout randomization (ASLR)
• Heap randomization
• Stack randomization

The article went on to say that "...some of these defenses are in the core operating system, and the Microsoft Visual C++ compiler offers others" but didn't explain how these strategies would actually increase security.

Anyone know why memory randomization increases security, if at all? Do other platforms and compilers employ similar strategies?

Answer 1

It increases security by making it hard to predict where something will be in memory. Quite a few buffer overflow exploits work by putting (for example) the address of a known routine on the stack, and then returning to it. It's much harder to do that without knowing the address of the relevant routine.

As far as I know, OpenBSD was about the first to do this, at least among the reasonably well-known OSes for PCs.