I believe this requires the attacker to have access to the ASR neural net's weights, so Mozilla's seems like the only popular framework that's vulnerable right now (not that I'm opposed to them keeping things open).
This is exactly why we need to keep ASR tech open. These kinds of issues affect DNNs in general, and other ASR engines based on them are also vulnerable. Having models and the data used to train them open is a great way to help academia make progress in this space.
Adversarial examples don’t actually have to be generated with the same neural network. If you want to attack another NN, you can make your own with similar training data and similar structure and the attacks can carry over to some extent.