Nick Wilson discovered a security issue that affects Flow when used with
caching proxies such as Varnish:
https://phabricator.wikimedia.org/T116095 (this task will be opened soon).
In such a setup, topics in cache would remain accessible after the board
was deleted.
We have deployed the fix to the cluster and merged it to the Flow
repository.
Let us know if you are using REL1_24 or REL1_25 of Flow and this issue
affects you.
Thanks,
Matt Flaschen