Does gaining control of a creature also give you control of auras attached to it?

When you gain control of a creature, you become that creature's controller, but any Auras enchanting it remain under their current controller's control. Control of an Aura is determined independently from the object it's attached to. This is established in CR 303.4e, which clarifies that an Aura's controller is not required to be the controller of the enchanted permanent.

This means an opponent's Aura (say, a removal-style enchantment like Pacifism) that was attached to a creature you steal will still be controlled by your opponent. Conversely, a beneficial Aura you own that was on your opponent's creature will remain under your control after you steal the creature.

It's also worth noting that if an Aura's enchantment condition is violated (e.g., it can only enchant creatures your opponent controls and you take the creature), the Aura is put into its owner's graveyard as a state-based action per CR 704.5n — but that is a separate issue from control.

Concrete example: Your opponent controls a Grizzly Bears enchanted with their own Rancor. You cast Act of Treason, gaining control of the Bears until end of turn. Your opponent still controls Rancor — the Bears just happen to have trample and +2/+0 while you control them.