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


- **Severity:** Medium 6.3 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 21 Oct 2026
- **Updated:** 28 Oct 2026
- **Also known as:** GHSA-6j8p-r676-fv69, GHSA-mr6r-mvw4-736g

## What is CVE-2020-37289?

CVE-2020-37289 is a medium-severity vulnerability in vyperlang vyper, published on 21 Oct 2026. 

### Official 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.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2020-37289?

2 open source packages ship an affected version, including vyper.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `vyper` | PyPI | All versions to 0.1.0b16 | None |
| `vyper` | PyPI | All versions to 0.1.0b16 | None |

## How do I fix CVE-2020-37289?

No fix has been published for CVE-2020-37289 yet. Limit exposure of the affected software until one is available.

## Is CVE-2020-37289 being exploited?

There is no known exploitation of CVE-2020-37289 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-37289 and fix it if it is affected.

What it is: CVE-2020-37289 is a medium-severity vulnerability in vyperlang vyper, published on 21 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2020-37289 in the wild and no public exploit code.

Affected packages and fixed versions:
- vyper (PyPI): affected all versions up to 0.1.0b16; no fix listed
- vyper (PyPI): affected all versions up to 0.1.0b16; no fix listed

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2020-37289/ (Markdown: https://insights.sbomify.com/CVE-2020-37289/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-37289
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-37289
- OSV: https://osv.dev/vulnerability/CVE-2020-37289

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-37289/
Summaries are generated and may contain mistakes; the official description above is the record.