Hash collision attack in PHP

Question

PHP

Can someone explain in a simple and understandable way what a hash collision attack is, how it manifests itself in PHP before version 5.3.9, and what it threatens?

Answer 1

habrahabr.ru/blogs/infosecurity/135530/
The article contains general words, and in the comments - explanations on the fingers.

Answer 2

This, apparently, is a kind of attack when such data is sent to the script as input, which, when parsing parameters or further processing, forms many hash function collisions. As a result, arrays containing this data start to work terribly slowly. Those. It turns out this is a kind of DoS attack. Why it threatens PHP up to version 5.3.9, I don't know. Perhaps a simple hash function was used there, to which it is easy to pick up collisions.

Answer 3

nikic.github.com/2011/12/28/Supercolliding-a-PHP-array.html Threatens
- transferring about 60,000 elements to an array can take up to 30 seconds (worst case).