GHSA-vg88-3v92-rjx2 Vyper: Return inside for loop more than 1 level deep

• PyPI vyper: >= 0.1.0b10, < 0.2.3 → fixed in 0.2.3

VVE-2020-0002 Earlier today, we received a responsible disclosure of a potential issue from @michwill (developer of @curvefi) for Vyper users who use return statements inside for loops of nested internal calls. Returning inside a for loop causes an invalid jump dest, reverting the transaction unnecessarily. MWE: ```python @internal def _baz(): for i in range(1): return # Stack underflow happens here @internal def _bar(): self._baz() @external def foo(): self._bar() ``` Impact Impact is minor, it is unlikely a user would encounter this problem unless they were working with nested calls, and return statements inside calls. Even in that scenario, you would encounter a revert which should be noticeable with adequate testing. In limited circumstances, this could cause a DoS attack for public contracts under certain conditions. Patches Fixed in https://github.com/vyperlang/vyper/pull/2110. Please upgrade to Vyper 0.2.3 Workarounds Not returning inside a for loop nested 2+ internal calls deep works as is: ```python @internal def _baz(): for i in range(1): pass return # This works fine @internal def _bar(): self._baz() @external def foo(): self._bar() ``` For more information If you have any questions or comments about this advisory: • Chat with us in our gitter • Open an issue in https://github.com/vyperlang/vyper • Email us at [email protected]