[Python-Dev] Negative times behaviour in itertools.repeat for Python maintenance releases (2.7, 3.3 and maybe 3.4)

Alexander Belopolsky alexander.belopolsky at gmail.com
Mon Jan 27 04:51:20 CET 2014

On Sun, Jan 26, 2014 at 12:00 PM, Vajrasky Kok
<sky.kok at speaklikeaking.com>wrote:

> >>> repeat('a', times=-1)
> repeat('a')

As I think about it, this may be more than a bug but a door for a denial of
service attack.   Imagine an application where times comes from an
untrusted source.  Someone relying on documented behavior may decide to
sanitize the value by only checking against an upper bound assuming that
negative values would just lead to no repetitions.  If an attacker could
somehow case times to get the value of -1 this may cause an infinite loop,
blow up memory etc.

If you think this is far-fetched - consider a web app that uses repeat() as
a part of logic to pretty-print user input.  The times value may come from
a calculation of a difference between the screen width and the length of
some string - both under user control.

So maybe the fix should go into security bugs only branches as well.
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