Until very recently, memory allocators were more than happy to return you the thing you just deallocated if you asked for another allocation of the same size. It makes sense, too: if you're calling malloc/free in a loop, which is pretty common, this is pretty much the best thing you can do for performance. Countless heap exploits later (mostly attacking heap metadata rather than stale data, to be honest) allocators have begun to realize that predictable allocation patterns might not be the best idea, so they're starting to move away from this.

Ah, good point; at the very least things like zeroing out buffers upon deallocation would have helped. Yes, I was a fan of the commits showing up at opensslrampage.org. One of the highlights was when they found it would use private keys as an entropy source: https://opensslrampage.org/post/83007010531/well-even-if-tim...

That's what happens by using normal malloc/free anyway, no? Implementations of malloc have a strong performance incentive to allocate from the cache hot most recently freed blocks.