What’s Vulnerable › Vulnerabilities

CVE-2023-46247: Vyper has incorrect storage layout for contracts containing large arrays

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.7% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2023-12-13 · updated 2026-06-17
• Weakness: CWE-193

Description

Vyper is a Pythonic Smart Contract Language for the Ethereum Virtual Machine (EVM). Contracts containing large arrays might underallocate the number of slots they need by 1. Prior to v0.3.8, the calculation to determine how many slots a storage variable needed used `math.ceil(type_.size_in_bytes / 32)`. The intermediate floating point step can produce a rounding error if there are enough bits set in the IEEE-754 mantissa. Roughly speaking, if `type_.size_in_bytes` is large (> 2**46), and slightly less than a power of 2, the calculation can overestimate how many slots are needed by 1. If `type_.size_in_bytes` is slightly more than a power of 2, the calculation can underestimate how many slots are needed by 1. This issue is patched in version 0.3.8.

Affected products

• vyperlang vyper: before 0.3.8 — fixed in 0.3.8

How to fix

Upgrade to a fixed version: vyperlang vyper 0.3.8. Check the vendor advisory for mitigations.

References

• https://github.com/vyperlang/vyper/blob/6020b8bbf66b062d299d87bc7e4eddc4c9d1c157/vyper/semantics/validation/data_positions.py#L197
• https://github.com/vyperlang/vyper/commit/0bb7203b584e771b23536ba065a6efda457161bb
• https://github.com/vyperlang/vyper/security/advisories/GHSA-6m97-7527-mh74
• https://github.com/vyperlang/vyper/blob/6020b8bbf66b062d299d87bc7e4eddc4c9d1c157/vyper/semantics/validation/data_positions.py#L197
• https://github.com/vyperlang/vyper/commit/0bb7203b584e771b23536ba065a6efda457161bb
• https://github.com/vyperlang/vyper/security/advisories/GHSA-6m97-7527-mh74

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