---
title: "CVE-2024-24563: Vyper negative array index bounds checks"
url: https://erroneo.us/security/cve/CVE-2024-24563/
description: "CVE-2024-24563 (vyper (PyPI)): Vyper is a Pythonic Smart Contract Language for the Ethereum Virtual Machine. Arrays can be keyed by a signed integer, while…"
type: vulnerability-record
section: "Security Digest"
date_published: 2024-02-07
date_modified: 2025-06-17
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2024-24563"
kev: false
cvss: 9.8
epss: 0.01539
license: All rights reserved. Quote with attribution and a link.
---

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

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Not in CISA KEV , but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 1.5% , percentile 75: FIRST’s model estimates a 1.5% chance of exploitation activity in the next 30 days, higher than 75% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes vyper (PyPI) < 0.4.0, fixed in 0.4.0 . Check your lockfile, including transitive dependencies.

## What it is

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 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.

## Affected packages

- PyPI `vyper` < 0.4.0 → fixed: 0.4.0

## Affected products (CVE record)

- vyperlang vyper: <= 0.3.10

## Severity

- GitHub_M CVSS 3.1: 9.8 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`
- GitHub CVSS 3.1: 9.8 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc , automatable no , technical impact total .
- FIRST EPSS (model of 2026-10-21): 1.54% probability of exploitation activity in the next 30 days; percentile 75.

## Sources

- [GitHub Advisory GHSA-52xq-j7v9-v4v2](https://github.com/advisories/GHSA-52xq-j7v9-v4v2)
- [CVE.org record CVE-2024-24563](https://www.cve.org/CVERecord?id=CVE-2024-24563)
- [NVD entry CVE-2024-24563](https://nvd.nist.gov/vuln/detail/CVE-2024-24563)
- [github.com](https://github.com/vyperlang/vyper/security/advisories/GHSA-52xq-j7v9-v4v2)
- [github.com](https://github.com/vyperlang/vyper/blob/a1fd228cb9936c3e4bbca6f3ee3fb4426ef45490/vyper/codegen/core.py#L534-L541)
- [github.com](https://github.com/vyperlang/vyper/blob/c150fc49ee9375a930d177044559b83cb95f7963/vyper/semantics/types/subscriptable.py#L127-L137)
- [github.com](https://github.com/pypa/advisory-database/tree/main/vulns/vyper/PYSEC-2024-150.yaml)

---
Source page: https://erroneo.us/security/cve/CVE-2024-24563/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt