OpenBSD's buitl-in memory leak detection
Since 2007 I have been working on and off on the malloc(3) implementation in OpenBSD. OpenBSD's malloc is a bit of a different beast compared to most other implementations: it has built-in, always-on randomization, it returns pages to the operating system when it no longer needs them and performs extensive consistency checking. These features help a lot when debugging memory management problems in programs and make various forms of heap based attacks much harder. You can find more details in the sheets of the presentation I gave on EuroBSDCon 2009.
Quote from a private correspondence with a Qualys vulnerability researcher (used with permission):
> Interesting (great malloc by the way, clean design and implementation
> and lots of security checks)!