CVE-2020-37289: Vyper before 0.3.1 Improper Input Validation of uint8 Interface Return Values

Severity: low (CVSS 3.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-21 · updated 2026-10-28
Weakness: CWE-20

Description

Vyper before 0.3.1 lacks a uint8 type, allowing interface return values declared as uint8, such as ERC20.decimals(), to be stored in uint256 variables without bounds checking. Malicious contracts can return values greater than 255 to manipulate or bypass contract logic that relies on these values.

Affected products

vyperlang vyper: before 0.3.1 — fixed in 0.3.1

How to fix

Upgrade to a fixed version: vyperlang vyper 0.3.1. Check the vendor advisory for mitigations.

References

https://github.com/vyperlang/vyper/security/advisories/GHSA-mr6r-mvw4-736g
https://www.vulncheck.com/advisories/vyper-before-0.3.1-improper-input-validation-of-uint8-interface-return-values

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