Vyper: incorrect order of evaluation of side effects for some builtins

Vulnerability Description

Vyper is a Pythonic Smart Contract Language. In affected versions the order of evaluation of the arguments of the builtin functions `uint256_addmod`, `uint256_mulmod`, `ecadd` and `ecmul` does not follow source order. This behaviour is problematic when the evaluation of one of the arguments produces side effects that other arguments depend on. A patch is currently being developed on pull request #3583. When using builtins from the list above, users should make sure that the arguments of the expression do not produce side effects or, if one does, that no other argument is dependent on those side effects.

References

• https://github.com/vyperlang/vyper/security/advisories/GHSA-4hg4-9mf5-wxxq
• https://github.com/vyperlang/vyper/pull/3583