[Openstack-security] [Bug 1757300] Fix proposed to heat (stable/pike)
Fix proposed to branch: stable/pike
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RandomString may have less entropy than expected
Status in OpenStack Heat:
Status in OpenStack Security Advisory:
When generating a random string, once we have selected from the
various required pools, we continue by selecting a pool at random and
then selecting a character from that pool at random. This does not
take into account the differing sizes of the available pools, nor the
fact that the same character could appear in multiple pools. This
results in a non-uniform probability distribution of characters.
For example, in the following resource:
- class: lettersdigits
- sequence: "*$"
one might reasonably expect to find an average of 3 '*' or '$'
characters in the output, but in fact there would be an average of 33.
Since users mostly make use of this feature to generate default
passwords for services they are deploying, this would result in the
generated passwords having slightly less entropy than expected.
Pathological cases where the entropy is massively reduced (like the
one above - where it is only 229.5 bits vs. the expected 391 bits) are
possible, although it's probably unlikely that users would encounter
them by accident.
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