perl -- denial of service via algorithmic complexity attack on hashing routines

Perl developers report:

In order to prevent an algorithmic complexity attack
against its hashing mechanism, perl will sometimes
recalculate keys and redistribute the contents of a hash.
This mechanism has made perl robust against attacks that
have been demonstrated against other systems.
Research by Yves Orton has recently uncovered a flaw in
the rehashing code which can result in pathological
behavior. This flaw could be exploited to carry out a
denial of service attack against code that uses arbitrary
user input as hash keys.
Because using user-provided strings as hash keys is a
very common operation, we urge users of perl to update their
perl executable as soon as possible.