# CVE-2023-42460: _abi_decode input not validated in complex expressions in Vyper

> Vyper compiler fails to validate _abi_decode inputs in nested expressions, allowing bounds checking bypass and incorrect contract results.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 26 Sep 2023
- **Updated:** 24 Sep 2024
- **Also known as:** GHSA-cx2q-hfxr-rj97, PYSEC-2023-191

## What is CVE-2023-42460?

CVE-2023-42460 is a medium-severity vulnerability in vyperlang vyper, published on 26 Sep 2023. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Vyper is a Pythonic Smart Contract Language for the EVM. The `_abi_decode()` function does not validate input when it is nested in an expression. Uses of `_abi_decode()` can be constructed which allow for bounds checking to be bypassed resulting in incorrect results. This issue has not yet been fixed, but a fix is expected in release `0.3.10`. Users are advised to reference pull request #3626.

Weakness: CWE-682 (Incorrect Calculation)

## Which versions are affected by CVE-2023-42460?

3 open source packages ship an affected version, including vyper. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `vyper` | PyPI | From 0.3.4 | 0.3.10 |
| `vyper` | PyPI | From 0.3.4 | 0.3.10 |
| `vyper` | PyPI | From 0.3.4 | 0.3.10 |

Products: Vyperlang Vyper.

## How do I fix CVE-2023-42460?

Upgrade vyper to 0.3.10 or later.

## Is CVE-2023-42460 being exploited?

There is no known exploitation of CVE-2023-42460 in the wild and no public exploit code.

## Other vulnerabilities in vyperlang vyper

- [CVE-2024-24563](https://insights.sbomify.com/CVE-2024-24563/): Vyper array negative index vulnerability (critical 9.8)
- [CVE-2024-24561](https://insights.sbomify.com/CVE-2024-24561/): Vyper bounds check on built-in `slice()` function can be overflowed (critical 9.8)
- [CVE-2023-39363](https://insights.sbomify.com/CVE-2023-39363/): Vyper incorrectly allocated named re-entrancy locks (critical 9.1)
- [CVE-2022-24845](https://insights.sbomify.com/CVE-2022-24845/): Integer bounds error in Vyper (high 8.8)
- [CVE-2022-29255](https://insights.sbomify.com/CVE-2022-29255/): Multiple evaluation of contract address in call in vyper (high 8.2)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-42460 and fix it if it is affected.

What it is: CVE-2023-42460 is a medium-severity vulnerability in vyperlang vyper, published on 26 Sep 2023. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2023-42460 in the wild and no public exploit code.

Affected packages and fixed versions:
- vyper (PyPI): affected from 0.3.4; fixed in 0.3.10
- vyper (PyPI): affected from 0.3.4; fixed in 0.3.10
- vyper (PyPI): affected from 0.3.4; fixed in 0.3.10

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-2023-42460/ (Markdown: https://insights.sbomify.com/CVE-2023-42460/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-42460
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-42460
- OSV: https://osv.dev/vulnerability/CVE-2023-42460

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-42460/
Summaries are generated and may contain mistakes; the official description above is the record.