# CVE-2024-24560: Vyper's external calls can overflow return data to return input buffer

Source: https://junglewise.ai/threats/cve-2024-24560-vyper-s-external-calls-can-overflow-return-data-to-return-input  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2024-02-02  
License: CC BY 4.0 with a link back

CVE-2024-24560 · Severity: low · CVSS 3.1 · Published 2024-02-02

Vyper is a Pythonic Smart Contract Language for the Ethereum Virtual Machine. When calls to external contracts are made, we write the input buffer starting at byte 28, and allocate the return buffer to start at byte 0 (overlapping with the input buffer). When checking RETURNDATASIZE for dynamic types, the size is compared only to the minimum allowed size for that type, and not to the returned value's length. As a result, malformed return data can cause the contract to mistake data from the input buffer for returndata.  When the called contract returns invalid ABIv2 encoded data, the calling contract can read different invalid data (from the dirty buffer) than the called contract returned.

Technologies: [vyper (PyPI)](https://junglewise.ai/threats/technologies/vyper). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2024-24560 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2024-24560 being exploited in the wild.

**How severe is CVE-2024-24560?** Low severity, with a CVSS score of 3.1, published 2 February 2024.

**Which products and versions are affected?** vyper (PyPI) ECOSYSTEM:introduced=0,fixed=0.4.0, ECOSYSTEM:introduced=0,fixed=0.4.0b1.

**Is there a fix for CVE-2024-24560?** Yes. vyper (PyPI): upgrade to 0.4.0, 0.4.0b1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2024-24560?** Check whether you run vyper (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- vyper (PyPI): upgrade to 0.4.0, 0.4.0b1 or later

  ```sh
  pip install "vyper>=0.4.0b1"
  ```


## Affected products

- vyper (PyPI) ECOSYSTEM:introduced=0,fixed=0.4.0, ECOSYSTEM:introduced=0,fixed=0.4.0b1

## Identifiers

- CVE-2024-24560
- GHSA-gp3w-2v2m-p686
- PYSEC-2024-148

## Related threats

- [Vyper memory corruption in nested function calls and tuples](https://junglewise.ai/threats/vyper-memory-corruption-using-function-calls-within-tuples-nested-calls-c0689acb)
- [Vyper stack corruption in complex type argument passing](https://junglewise.ai/threats/vyper-call-stack-corruption-when-passing-complex-type-containing-non-3deb0c30)
- [Vyper return statement in nested for loops causes revert](https://junglewise.ai/threats/vyper-return-inside-for-loop-more-than-1-level-deep-ee8a193d)
- [PYSEC-2026-2028 - Vyper's `slice()` may elide side-effects when output length is 0](https://junglewise.ai/threats/cve-2025-47774-vyper-s-slice-may-elide-side-effects-when-output-length-is-0)
- [PYSEC-2026-2029 - Vyper's `concat()` builtin may elide side-effects for zero-length arguments](https://junglewise.ai/threats/cve-2025-47285-vyper-s-concat-builtin-may-elide-side-effects-for-zero-length)