---
id: CVE-2026-123561
title: >-
  Sveltejs devalue before 5.9.3 __proto__ Rejection Bypass via Property-Key
  Coercion
summary: >-
  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 wit…
severity: low
cvss: 3.7
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N'
cvssSource: cna
cwe:
  - CWE-1321
vendor: sveltejs
product: devalue
affected:
  - devalue < 5.9.3
published: '2026-11-08'
updated: '2026-11-08'
sourceUpdated: '2026-11-08T01:38:01.726Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-123561'
references:
  - url: >-
      https://github.com/sveltejs/devalue/security/advisories/GHSA-4q55-j62x-fr9h
    label: GitHub Security Advisory (GHSA-4q55-j62x-fr9h)
  - url: >-
      https://www.vulncheck.com/advisories/sveltejs-devalue-before-5.9.3-proto-rejection-bypass-via-property-key-coercion
    label: >-
      VulnCheck Advisory: Sveltejs devalue before 5.9.3 __proto__ Rejection
      Bypass via Property-Key Coercion
tags:
  - cve.org
ingestedAt: '2026-11-08T02:43:18.661Z'
---

## Overview

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.

## Affected

- `devalue < 5.9.3`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.