Do whitening mouth washes aggravate cavities?

No: Cavities are caused by bacteria. If you already have a cavity, whitening mouth washes will not by itself aggravate the cavity.

Maybe...?: The mouthwash may irritate an existing cavity, due to the thermal difference or irritation from the bleaching agent. This will be felt as some version of pain in the tooth affected. It will not cause a new cavity to form. You should see your dentist for a check up and cleaning to put your mind to rest.

Maybe: It is very possible that they do. See a dentist for proper diagnosis and treatment.

Whitening rinses: In my opinion, whitening rinses do little or nothing to actually whiten teeth. Whatever whitening agents they have are a low concentration and stay in contact with teeth too short a time for any substantial whitening. If you want your teeth whiter, speak to your dentist for better alternatives. If you have cavities, erosions or defective restorations, you might have more sensitivity using them.