Gregory's Server@j12t almost certainly this is again not an attack on Signal itself, but instead an attack on the underlying system.
It's magnitudes more likely that there is a flaw in for example Android that allows for exploitation on the underlying system. And once the base system is fully or partially compromised, you get access to things on it.
Such point has been raised before, and every time it was either a compromise of the base system or just FUD, never a compromise of Signal itself.
@cherti This would be my suspicion as well, but my beef is with the author who insinuates something that could be important without being precise about it and without any sources. That is not helpful except to make the author seem to be in the know by people who don't know any better, or to seed FUD.