Headline
CVE-2023-32675: nonpayable default functions can sometimes be sent ether with calldatasize<4
Vyper is a pythonic Smart Contract Language for the ethereum virtual machine. In contracts with more than one regular nonpayable function, it is possible to send funds to the default function, even if the default function is marked nonpayable. This applies to contracts compiled with vyper versions prior to 0.3.8. This issue was fixed by the removal of the global calldatasize check in commit 02339dfda. Users are advised to upgrade to version 0.3.8. Users unable to upgrade should avoid use of nonpayable default functions.
Impact
in contracts with at least one regular nonpayable function, due to the callvalue check being inside of the selector section, it is possible to send funds to the default function by using less than 4 bytes of calldata, even if the default function is marked nonpayable. this applies to contracts compiled with vyper<=0.3.7.
# @version 0.3.7
# implicitly nonpayable @external def foo() -> uint256: return 1
# implicitly nonpayable @external def __default__(): # could receive ether here pass
Patches
this was fixed by the removal of the global calldatasize check in 02339df.
Workarounds
don’t use nonpayable default functions
References
Are there any links users can visit to find out more?
Related news
### Impact in contracts with at least one regular nonpayable function, due to the callvalue check being inside of the selector section, it is possible to send funds to the default function by using less than 4 bytes of calldata, even if the default function is marked `nonpayable`. this applies to contracts compiled with vyper<=0.3.7. ```vyper # @version 0.3.7 # implicitly nonpayable @external def foo() -> uint256: return 1 # implicitly nonpayable @external def __default__(): # could receive ether here pass ``` ### Patches this was fixed by the removal of the global calldatasize check in https://github.com/vyperlang/vyper/commit/02339dfda0f3caabad142060d511d10bfe93c520. ### Workarounds don't use nonpayable default functions ### References _Are there any links users can visit to find out more?_