# 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](https://pypi.org/project/vyper/)
### 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 ](https://gitter.im/vyperlang/community)
* Open an issue in [https://github.com/vyperlang/vyper](https://github.com/vyperlang/vyper)
* Email us at [
[email protected]](mailto:
[email protected])
