CVE-2023-30837Public exploitNetwork attack vector

Contract ownership overwrite via storage-slot wraparound

Published May 8, 2023 · Updated Jan 29, 2025

Storage allocation overflow in Vyper before 0.3.8 allows remote attackers to overwrite variables in compiled smart contracts via calldata. The compiler's storage allocator accepts an array extending beyond the 2^256-slot boundary, so generated modular pointer arithmetic wraps a large index onto earlier storage. A deployed contract must contain such an oversized array and an externally callable indexed write; crafted calldata then changes protected state, including ownership.

CVSS severity7.5
High
EPSS probability0.70%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Storage allocation overflow in Vyper before 0.3.8 allows remote attackers to overwrite variables in compiled smart contracts via calldata. The compiler's storage allocator accepts an array extending beyond the 2^256-slot boundary, so generated modular pointer arithmetic wraps a large index onto earlier storage. A deployed contract must contain such an oversized array and an externally callable indexed write; crafted calldata then changes protected state, including ownership.

The record

CVE
CVE-2023-30837
Published
May 8, 2023
Updated
Jan 29, 2025
Vendor
Vyper
Product
Vyper
Classifications
CWE-789, T1565.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 8, 2023CVE publishedPublication date reported by the CVE source.
  2. Jan 29, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 0.3.8

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Vyper · Vyperversion=< 0.3.8

Published CVSS scores

7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
7.5GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-789Memory Allocation with Excessive Size Value
T1565.001Stored Data Manipulation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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