However this does not prevent any of your employees or other users of systems with access to use spipped from committing this attack. You still need a client somewhere and the server is still vulnerable.
Allowing remote connections from any IP to your database, like heroku apparently does, sounds kind of crazy to me. I can't believe they do it. But limiting and encrypting that access just limits, and does not eliminate your vulnerability to this bug.
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Just to be really clear: Say your corporate blog stores it’s data in your main Postgres instance. As blogging engines tend to, it has a bug, and hackers succeed in using that to get access to your blog’s server. Even if you are using spiped to connect the 2 boxes they still have the ability to mess with your main database, on some other, probably much better secured, box. This bug is ugly.