GHSA-vg88-3v92-rjx2

Vyper: Return inside for loop more than 1 level deep

Risk score: 43/100
CVSS: 6.3 v4.0
Published: 6 Oct 2026

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What to know

What it is: 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 de…
Affected: vyper (pip) >= 0.1.0b10, < 0.2.3
Fix: Upgrade vyper to 0.2.3 or later.
Exploitation: No known exploitation

Story map

Story map: the flaws, the fix, how it unfolded and what it connects to. Boxes link to the record or article.

At a glance

vyper: Yellow, plan it in. When performing a function call inside a tuple or as an argument inside another function call, there is a memory corruption issue that occurs because of an incorrect pointer to the the tip of the stack. Example code: python @internal def _foo(a: uint256, b: uint256, c: uint256) -> (uint256, uint256, uint256, uint256, …

The flaws

GHSA-vg88-3v92-rjx2: Vyper: Return inside for loop more than 1 level deep (CVSS 6.3)
GHSA-2r3x-4mrv-mcxf: Vyper: Memory corruption using function calls within tuples / nested calls (CVSS 6.9)
GHSA-4v7v-gqf9-ww2g: Vyper: Call stack corruption when passing complex type containing non-base type members as argument (CVSS 6.9)

The fix

Fix: Upgrade vyper to 0.2.6 or later.

Who is exposed: vyper (pip) < 0.2.6

Where it stands

No known exploitation

Connects to

Same weakness: CWE-691 (CWE-691). 2 other warnings in 30 days

Why it is Yellow

CVSS 6.3 medium
On your watchlist: PyPI

Affected packages

Package	Ecosystem	Vulnerable	Fixed in
vyper	pip	>= 0.1.0b10, < 0.2.3	0.2.3

References

Original description

# 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 [security@vyperlang.org](mailto:security@vyperlang.org)

Last activity 6 Oct 2026. Patch Forecast updates every hour.