# GHSA-4q55-j62x-fr9h: devalue: Malformed null-prototype object keys bypass __proto__ rejection via property-key coercion

> Malformed keys in devalue bypass __proto__ rejection, potentially allowing prototype pollution, though impact is deemed unlikely.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 1 Oct 2026

## What is GHSA-4q55-j62x-fr9h?

GHSA-4q55-j62x-fr9h is a vulnerability in devalue, published on 1 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

This is another instance of https://github.com/sveltejs/devalue/security/advisories/GHSA-mwv9-gp5h-frr4, where some payloads could cause `parse` to create objects with a `__proto__` own property. This on its own is not enough to cause prototype pollution, and indeed this is actually how `JSON.parse` works, but we decided to be a little more defensive here and not allow the creation of objects with `__proto__` own-properties. It is very unlikely for this to cause any issues.

## Which versions are affected by GHSA-4q55-j62x-fr9h?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `devalue` | npm | All versions | 5.9.3 |
| `devalue` | npm | All versions | 5.9.3 |

## How do I fix GHSA-4q55-j62x-fr9h?

Upgrade devalue to 5.9.3 or later.

## Is GHSA-4q55-j62x-fr9h being exploited?

There is no known exploitation of GHSA-4q55-j62x-fr9h in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for GHSA-4q55-j62x-fr9h and fix it if it is affected.

What it is: GHSA-4q55-j62x-fr9h is a vulnerability in devalue, published on 1 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of GHSA-4q55-j62x-fr9h in the wild and no public exploit code.

Affected packages and fixed versions:
- devalue (npm): affected all versions; fixed in 5.9.3
- devalue (npm): affected all versions; fixed in 5.9.3

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/GHSA-4q55-j62x-fr9h/ (Markdown: https://insights.sbomify.com/GHSA-4q55-j62x-fr9h/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/GHSA-4q55-j62x-fr9h

---
From sbomify Insights: https://insights.sbomify.com/GHSA-4q55-j62x-fr9h/
Summaries are generated and may contain mistakes; the official description above is the record.