But that doesn't have anything to do with what UX designers typically do
Software security and quality is the responsibility of everyone on the team. A good UX designer should be thinking of ways a user can escape the typical flow or operate in unintended ways and express that to testers. And in decisions where management is forcing untested patches everyone should chime in.
Granted, a company that isn’t focused on the user experience as much as it is on other things might not prioritise this as much in the first place.
I bet my ass UX is not anywhere close to the low-level OS team.
UX is definitely embedded in the App level team but not in low-level.