# CVE-2024-24563: Vyper negative array index bounds checks

Source: https://junglewise.ai/threats/cve-2024-24563-vyper-negative-array-index-bounds-checks  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2024-02-07  
License: CC BY 4.0 with a link back

CVE-2024-24563 · Severity: low · CVSS 3.1 · Published 2024-02-07

Vyper is a Pythonic Smart Contract Language for the Ethereum Virtual Machine. Arrays can be keyed by a signed integer, while they are defined for unsigned integers only. The typechecker doesn't throw when spotting the usage of an `int` as an index for an array. The typechecker allows the usage of signed integers to be used as indexes to arrays. The vulnerability is present in different forms in all versions, including `0.3.10`. For ints, the 2's complement representation is used. Because the array was declared very large, the bounds checking will pass Negative values will simply be represented as very large numbers. As of time of publication, a fixed version does not exist.

There are three potential vulnerability classes: unpredictable behavior, accessing inaccessible elements and denial of service. Class 1: If it is possible to index an array with a negative integer without reverting, this is most likely not anticipated by the developer and such accesses can cause unpredictable behavior for the contract. Class 2: If a contract has an invariant in the form `assert index < x`, the developer will suppose that no elements on indexes `y | y >= x` are accessible. However, by using negative indexes, this can be bypassed. Class 3: If the index is dependent on the state of the contract, this poses a risk of denial of service. If the state of the contract can be manipulated in such way that the index will be forced to be negative, the array access can always revert (because most likely the array won't be declared extremely large). However, all these the scenarios are highly unlikely. Most likely behavior is a revert on the bounds check.

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

## Quick answers

**Is CVE-2024-24563 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2024-24563 being exploited in the wild.

**How severe is CVE-2024-24563?** Low severity, with a CVSS score of 3.1, published 7 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-2024-24563?** 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-2024-24563?** 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-2024-24563
- GHSA-52xq-j7v9-v4v2
- PYSEC-2024-150

## 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)