An integer overflow in the transferProxy function of a smart contract implementation for SmartMesh (aka SMT), an Ethereum ERC20 token, allows attackers to accomplish an unauthorized increase of digital assets via crafted _fee and _value parameters, as exploited in the wild in April 2018, aka the "proxyOverflow" issue.
https://www.reddit.com/r/ethereum/comments/8esyg9/okex_erc20_bug/