I don't think it'll be that bad:

1. The cost of running AI is dropping down to "free" - there's open weight models, open source tools, and guides on running your own if the long list of suppliers isn't good enough for your use cases.

2. Vulnerabilities have always been a risk; AI is not a panacea. The pre-AI best practices still apply. Furthermore, a huge percentage of vulnerabilities are in 3rd party tools and systems, which are systematically being scanned and fixed and/or exploited, then fixed.

You mention "the free software community" in your last sentence though - this implies the code in question is open source, so it's able to receive plenty of improvements from anyone with access to these tools.