{"id":"GHSA-vg88-3v92-rjx2","summary":"Vyper: Return inside for loop more than 1 level deep","details":"# VVE-2020-0002\nEarlier 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.\n\nMWE:\n```python\n@internal\ndef _baz():\n    for i in range(1):\n        return  # Stack underflow happens here\n\n@internal\ndef _bar():\n    self._baz()\n\n@external\ndef foo():\n    self._bar()\n```\n\n### Impact\nImpact 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.\n\n### Patches\nFixed in https://github.com/vyperlang/vyper/pull/2110. Please upgrade to [Vyper 0.2.3](https://pypi.org/project/vyper/)\n\n### Workarounds\nNot returning inside a for loop nested 2+ internal calls deep works as is:\n```python\n@internal\ndef _baz():\n    for i in range(1):\n        pass\n    return  # This works fine\n\n@internal\ndef _bar():\n    self._baz()\n\n@external\ndef foo():\n    self._bar()\n```\n\n### For more information\nIf you have any questions or comments about this advisory:\n* Chat with us in [our gitter ](https://gitter.im/vyperlang/community)\n* Open an issue in [https://github.com/vyperlang/vyper](https://github.com/vyperlang/vyper)\n* Email us at [security@vyperlang.org](mailto:security@vyperlang.org)","modified":"2026-10-06T15:30:03.643205761Z","published":"2026-10-06T15:20:10Z","database_specific":{"github_reviewed_at":"2026-10-06T15:20:10Z","nvd_published_at":null,"cwe_ids":["CWE-691"],"severity":"MODERATE","github_reviewed":true},"references":[{"type":"WEB","url":"https://github.com/vyperlang/vyper/security/advisories/GHSA-vg88-3v92-rjx2"},{"type":"WEB","url":"https://github.com/vyperlang/vyper/pull/2110"},{"type":"WEB","url":"https://github.com/vyperlang/vyper/commit/a1d92e5eb968a34a23850359656aee23334adb90"},{"type":"PACKAGE","url":"https://github.com/vyperlang/vyper"},{"type":"WEB","url":"https://github.com/vyperlang/vyper/releases/tag/v0.2.3"}],"affected":[{"package":{"name":"vyper","ecosystem":"PyPI","purl":"pkg:pypi/vyper"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0.1.0b10"},{"fixed":"0.2.3"}]}],"versions":["0.1.0b10","0.1.0b11","0.1.0b12","0.1.0b13","0.1.0b14","0.1.0b15","0.1.0b16","0.1.0b17","0.2.1","0.2.2"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-vg88-3v92-rjx2/GHSA-vg88-3v92-rjx2.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N"}]}