[Python-Dev] Hash collision security issue (now public)

Antoine Pitrou solipsis at pitrou.net
Thu Dec 29 12:10:00 CET 2011

On Thu, 29 Dec 2011 03:55:22 +0100
Christian Heimes <lists at cheimes.de> wrote:
> I've been dealing with web stuff and security for almost a decade. I've
> seen far worse attack vectors. This one can easily be solved with a
> couple of lines of Python code. For example Application developers can
> limit the maximum amount of POST parameters to a sensible amount and
> limit the length of each key, too.

Shouldn't the setting be implemented by frameworks?

> CPython could aid developers with a special subclass of dict. The
> crucial lookup function is already overwrite-able per dict instance and
> on subclasses of dict through PyDictObj's struct member PyDictEntry
> *(*ma_lookup)(PyDictObject *mp, PyObject *key, long hash). For example
> specialized subclass could limit the seach for a free slot to n
> recursions or choose to ignore the hash argument and calculate its own
> hash of the key.

Or, rather, the specialized subclass could implement hash randomization.



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