Coinbase solved a glitch that if exploited could allow undue balance credit of ETH accounts.
Researchers at VI Company found the security flaw and communicated with Coinbase.
As reported, before fixing the problem was that “By using a smart contract to distribute ether over a set of wallets you can manipulate the account balance of your Coinbase account. If 1 of the internal transactions in the smart contract fails all transactions before that will be reversed. But on Coinbase these transactions will not be reversed, meaning someone could add as much ether to their balance as they want. When you look up the Coinbase wallet address after this transaction you will see that it is empty, but checking your Coinbase wallet will show your funds.“