A vehicle includes a bulkhead elongated along an axis. The vehicle includes a base supported by the bulkhead and inflatable from a stowed position away from the bulkhead to a deployed position. The vehicle includes an airbag supported by the base and inflatable away from the bulkhead and the base to an inflated position, the airbag in the inflated position having a main portion and extensions extending away from the main portion along a vehicle-longitudinal axis, the extensions being spaced from each other along the axis.