just some observations since finding a cooperative Brazilian ATM for withdrawals from foreign accounts can be challenging (based on my experience.)

On my last two late night arrivals at GRU, the Banco24Horas ATM has been the only machine accepting foreign cards. That's unfortunate, because they seem to give lousy exchange rates (at all their ATMs), and charge a transaction fee to boot. The effective conversion rate was R$2.44. While this reflects their transaction fee, I do recall that their rate was still considerable lower than the interbank rates (which was R$2.64 on that date.)

I've had decent luck with finding Bradesco ATMs that work, but their rate still isn't spectacular-- on my recent trip, my transaction was processed at R$2.57 = 1 USD. (The interbank rate on that date was R$2.63.)

My best luck has been with Banco do Brasil -- my withdrawals through their ATMs were processed at R$2.64 and R$2.63 per USD -- the interbank rates were R$2.66 and R$2.65 on those dates.

As a last note -- I've never found a Banco Itaú ATM that has accepted my card.

My card has Cirrus, Plus, and Visa ATM access.