Advisory Weakness Curation

VVE-2021-0002: Incorrect `returndatasize` when using simple forwarder proxies deployed prior to EIP-1167 adoption ## Background @tjayrush reported a data handling issue with certain Web3 libraries using Vyper-deploy forwarder proxy contracts using our Vyper's built-in `create_forwarder_to` function prior to our change to support EIP-1167 style forwarder proxies. ### Impact If you are an end user of a forwarder-style proxy deployed using Vyper's built-in `create_forwarder_to` function AND you have a function that returns >4096 bytes AND you do no return data sanitation on the value returned, you could potentially see a data corruption issue. Otherwise, if you are handling the result of a return call AND you expect a specific `RETURNDATASIZE` that is less than 4096 (such as `SafeERC20.safeTransfer`) then the call will fail that check. ### Patches The issue was patched when we upgraded to EIP-1167 style forwarder proxies in #2281. ### Workarounds If you are making a call to a contract method that is expected to return <= 4096 bytes, there is no issue as the ABI decoders in both Solidity and Vyper will truncate the data properly. Web3 libraries will also do this, unless you are doing `eth_call` or `eth_sendTransaction` directly. If you are using a Solidity library that checks `RETURNDATASIZE` of an external call to a forwarder proxy deployed prior to this patch, it will fail on that assertion (such as `SafeERC20.safeTransfer`). The workaround is to always do a greater than or equal to check, rather than a strict equals to check.

VVE-2021-0002: Incorrect `returndatasize` when using simple forwarder proxies deployed prior to EIP-1167 adoption ## Background @tjayrush reported a data handling issue with certain Web3 libraries using Vyper-deploy forwarder proxy contracts using our Vyper's built-in `create_forwarder_to` function prior to our change to support EIP-1167 style forwarder proxies. ### Impact If you are an end user of a forwarder-style proxy deployed using Vyper's built-in `create_forwarder_to` function AND you have a function that returns bytes AND you do no return data sanitation on the value returned, you could potentially see a data corruption issue. Otherwise, if you are handling the result of a return call AND you expect a specific `RETURNDATASIZE` that is less than (such as `SafeERC20.safeTransfer`) then the call will fail that check. ### Patches The issue was patched when we upgraded to EIP-1167 style forwarder proxies in #2281. ### Workarounds If you are making a call to a contract method that is expected to return bytes, there is no issue as the ABI decoders in both Solidity and Vyper will truncate the data properly. Web3 libraries will also do this, unless you are doing `eth_call` or `eth_sendTransaction` directly. If you are using a Solidity library that checks `RETURNDATASIZE` of an external call to a forwarder proxy deployed prior to this patch, it will fail on that assertion (such as `SafeERC20.safeTransfer`). The workaround is to always do a greater than or equal to check, rather than a strict equals to check.