GHSA-VG88-3V92-RJX2
Vulnerability from github – Published: 2026-10-06 15:20 – Updated: 2026-10-06 15:20VVE-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:
@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:
@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 security@vyperlang.org
{
"affected": [
{
"package": {
"ecosystem": "PyPI",
"name": "vyper"
},
"ranges": [
{
"events": [
{
"introduced": "0.1.0b10"
},
{
"fixed": "0.2.3"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-691"
],
"github_reviewed": true,
"github_reviewed_at": "2026-10-06T15:20:10Z",
"nvd_published_at": null,
"severity": "MODERATE"
},
"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)",
"id": "GHSA-vg88-3v92-rjx2",
"modified": "2026-10-06T15:20:11Z",
"published": "2026-10-06T15:20:10Z",
"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"
}
],
"schema_version": "1.4.0",
"severity": [
{
"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",
"type": "CVSS_V4"
}
],
"summary": "Vyper: Return inside for loop more than 1 level deep"
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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