Just look at stuff like pip, npm or pretty much any "modern" package manager in use by developers - they're all pretty much designed to pull in a shitload of arbitrary unaudited and in some causes unauditable dependencies.
And nobody wants to listen. That's why I prefer to work in heavily regulated areas nowadays - that way I can shorten that discussion with "yeah, but regulatory requirements don't let us do that, sorry"
The absolute basic should be having a local archive of dependencies which at least received a basic sanity check, and updates or additions to that should review changes being added. CI gets access to that cache, but by itself does not have network access to make sure no random crap gets pulled into the build. You'd be surprised how many popular build systems can't do that at all, or only with a lot of workarounds.