No more risk than with any other breed. Depends on how they're trained, treated, and bred. If one or both of their parents are/were aggressive, the odds increase, but aggressiveness in their pups is not guaranteed.
So...This may be controversial, and its either politically incorrect or people accuse you of being a breed Nazi for it, but that isn't true.
Labrador Retrievers are bred to help hunt for ducks. That means they have to be obedient, love the water, and have a natural retrieve with a good nose.
Great Pyrenees are bred to protect livestock from predators on the range. That means they need to work indpendently, and be content alone watching over their charges, and do what must be done when something threatens their herd. It also means they bark a lot.
German Shepherds are largely bred as working dogs, to protect, work in close proximity to their handlers, and go in and bite and attack if they must.
You will note that while Police and Law Enforcement use Labs, Beagles, German Shorthairs, Bloodhounds, etc, for detection purposes, they use GSD's and Malinois for the dirty work.
Which means, that your learning curve in getting the dog where you need it to be is potentially a lot steeper. So keep that in mind. You are buying a dog that has the potential to do damage and may have a tougher time keeping it contained.
Of course, if you're a good dog owner, or a drill seargant, or my Mom, none of this will be a problem. But if you want a dog that you potty train, teach sit, and don't have as much to worry about, get something else. Labs, Poodles, Doodles, hounds, some terriers, most sporting breeds, many herding breeds, depending on the exercise and training you can provide, might be a better choice.