{"id":"CVE-2020-37288","aliases":["GHSA-vg88-3v92-rjx2"],"title":"Vyper: Return inside for loop more than 1 level deep","summary":"Vyper: Return inside for loop more than 1 level deep","severity":"medium","cvss":3.7,"cvssVector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L","vendor":"vyper","product":"vyper","ecosystem":"pip","affected":["vyper >= 0.1.0b10, < 0.2.3"],"patched":["vyper 0.2.3"],"published":"2026-10-06","updated":"2026-10-24","sourceUpdated":"2026-10-24T02:56:09.007506586Z","source":"OSV","sourceUrl":"https://osv.dev/vulnerability/GHSA-vg88-3v92-rjx2","references":[{"url":"https://github.com/vyperlang/vyper/security/advisories/GHSA-vg88-3v92-rjx2"},{"url":"https://github.com/vyperlang/vyper/pull/2110"},{"url":"https://github.com/vyperlang/vyper/commit/a1d92e5eb968a34a23850359656aee23334adb90"},{"url":"https://github.com/vyperlang/vyper"},{"url":"https://github.com/vyperlang/vyper/releases/tag/v0.2.3"},{"url":"https://www.vulncheck.com/advisories/vyper-0.1-0b10-before-0.2.3-invalid-jump-destination-via-return-in-nested-loops","label":"VulnCheck Advisory: Vyper 0.1.0b10 before 0.2.3 Invalid Jump Destination via Return in Nested Loops"}],"tags":["osv","pip","cve.org"],"epss":0.00347,"epssPercentile":0.28109,"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"partial","timestamp":"2026-10-21T14:24:52.054926Z"},"cvssSource":"cna","cwe":["CWE-670"],"ingestedAt":"2026-10-21T01:37:08.050Z","slug":"CVE-2020-37288","body":"## Overview\n\n# 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)\n\n## Affected packages\n\n- `vyper >= 0.1.0b10, < 0.2.3`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `vyper 0.2.3`","depth":"sunlit","depthScore":20,"depthScoreParts":{"impact":20.4,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[{"seq":228506,"id":"CVE-2020-37288","ts":1792843232931,"field":"severity","old":"low","new":"medium"}]}