# CVE-2020-37287: Vyper call stack corruption with complex type arguments

Source: https://junglewise.ai/threats/cve-2020-37287-vyper-before-0-2-6-contains-a-call-stack-corruption-vulnerability  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-21. Updated: 2026-10-21  
License: CC BY 4.0 with a link back

CVE-2020-37287 · Severity: medium · CVSS 5.9 · Published 2026-10-21

Vyper is a smart contract programming language that compiles to Ethereum bytecode. When passing multi-dimensional arrays or structs as function arguments, the compiler incorrectly corrupts the call stack, causing functions to receive and return wrong data. An attacker could exploit this to manipulate contract behavior or extract unintended values.

Technologies: [Vyper](https://junglewise.ai/threats/technologies/vyper-vyper). Vendors: [Vyper](https://junglewise.ai/threats/vendors/vyper).

## Quick answers

**Is CVE-2020-37287 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2020-37287 being exploited in the wild.

**How severe is CVE-2020-37287?** Medium severity, with a CVSS score of 5.9, published 21 October 2026.

**Which products and versions are affected?** Vyper before 0.2.6.

**Is there a fix for CVE-2020-37287?** Yes: fixed in 0.2.6. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2020-37287 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2020-37287?** Check whether you run Vyper at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in 0.2.6

## Technical details

The vulnerability is a call stack management bug in the Vyper compiler: it assumes all subtypes within arrays or structs occupy exactly 32 bytes, but this assumption is false for non-base types. When complex types are passed to internal or external functions, the compiler generates incorrect stack layout code, leading to data corruption. Exploitation requires the attacker to deploy a malicious contract or call a vulnerable contract with crafted arguments.

## Affected products

- Vyper Vyper before 0.2.6

## Timeline

- 2020-10-10: disclosed
- 2020-10-10: patched

## References

- [https://github.com/vyperlang/vyper/security/advisories/GHSA-4v7v-gqf9-ww2g](https://github.com/vyperlang/vyper/security/advisories/GHSA-4v7v-gqf9-ww2g)
- [https://www.vulncheck.com/advisories/vyper-before-0.2.6-call-stack-corruption-via-complex-type-function-arguments](https://www.vulncheck.com/advisories/vyper-before-0.2.6-call-stack-corruption-via-complex-type-function-arguments)

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