Dangerous or not, it depends on how many there are and if they are leaning in the same direction. If they are all equally tilted and in the same direction, the house might be on the way to wandering off... If there are only a few, and if they are tilted in a way that counteracts each other force-wise, you can probably leave it be.
Otherwise, you’ll need to lift with a jack and straighten them/ or cast new ones.
You can probably fix this yourself - read up on plinth casting by googling for a while, and get a solid jack at biltema.