---
id: "CVE-2026-123561"
page: "https://infrastack.ai/live/CVE-2026-123561"
kind: "vulnerability"
aliases: ["CVE-2026-123561"]
title: "devalue: crafted keys bypass __proto__ check in parse"
severity: "medium"
cvss: 6.3
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["devalue", "javascript", "npm", "package"]
not_affected_if: ["trusted-input-only"]
published_at: "2026-11-08T02:16:48+00:00"
first_seen_at: "2026-11-08T02:21:11+00:00"
updated_at: "2026-11-08T02:25:05+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-123561", "first_seen_at": "2026-11-08T02:21:11+00:00"}]
exploit_sources: []
---

# devalue: crafted keys bypass __proto__ check in parse

Link for people: https://infrastack.ai/live/CVE-2026-123561 (this .md is for agents)

devalue is a JavaScript library for serializing and parsing data, and before 5.9.3 a malformed null-prototype object key can slip past its __proto__ rejection during property-key coercion. The sources say this yields objects with an own __proto__ property, which by itself does not cause prototype pollution.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- `npm ls devalue` to find the installed version in each project
- Check the `devalue` version in `package-lock.json`, `pnpm-lock.yaml` or `yarn.lock`

## Fix

- devalue: move to `5.9.3` or later

## Timeline

- 2026-11-08T02:21:11+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-123561

## Documents

- [advisory] Vendor advisory: github.com https://github.com/sveltejs/devalue/security/advisories/GHSA-4q55-j62x-fr9h
- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/sveltejs-devalue-before-5.9.3-proto-rejection-bypass-via-property-key-coercion

## From the sources

devalue before 5.9.3 allows malformed null-prototype object keys to bypass parse's __proto__ rejection through property-key coercion, an incomplete fix for GHSA-mwv9-gp5h-frr4. Attackers can supply crafted payloads that yield objects with a __proto__ own property, which alone does not cause prototype pollution.

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_Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai_