We were getting routine audits from security companies as well as public universities around the world on our OSS healthcare project. I would say it did give us in some way a false sense of security as we had the belief that a lot of the major bugs were addressed. The last 6 months have been very eye opening as the slew of reports have been difficult due to how many there have been, even with all of the false positives there's been a lot of legitimate vulnerabilities. This has been taxing for us to go through (and humbling as well).
That said, if we were a closed source project, I don't know that our own tooling would have discovered all the issues using LLMs as we are seeing more and more creative ways of people exposing exploits that I never would have thought to put into the LLM prompts.
But would they be able to find those obscure exploits if they had no idea what your code looks like?
If all you had was an API endpoint, you wouldn’t realistically have any way of figuring out how the internals work and finding obscure exploits.