---
id: CVE-2026-50029
title: >-
  js-toml is a TOML parser for JavaScript, Prior to version 1.1.2, the
  interpreter checks whether a key already exists in a parser-built container
  with `if (object[key])` instead of `if (key in object)`
summary: >-
  js-toml is a TOML parser for JavaScript, Prior to version 1.1.2, the
  interpreter checks whether a key already exists in a parser-built container
  with `if (object[key])` instead of `if (key in object)`. When the prior value
  is a falsy pri…
severity: medium
cvss: 5.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N'
cwe:
  - CWE-697
vendor: js-toml
product: js-toml
affected:
  - js-toml <= 1.1.1
patched:
  - js-toml 1.1.2
published: '2026-08-14'
updated: '2026-09-18'
sourceUpdated: '2026-09-18T20:09:01.757'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-50029'
references:
  - url: >-
      https://github.com/sunnyadn/js-toml/commit/e0504fa5d3dcde2d1d588c9001c24b7b700beeeb
    label: security-advisories@github.com
  - url: 'https://github.com/sunnyadn/js-toml/releases/tag/v1.1.2'
    label: security-advisories@github.com
  - url: >-
      https://github.com/sunnyadn/js-toml/security/advisories/GHSA-m34p-749j-x6m6
    label: security-advisories@github.com
  - url: >-
      https://github.com/sunnyadn/js-toml/security/advisories/GHSA-m34p-749j-x6m6
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
  - url: 'https://github.com/advisories/GHSA-m34p-749j-x6m6'
tags:
  - nvd
  - ghsa
  - npm
epss: 0.00398
epssPercentile: 0.31202
ecosystem: npm
ingestedAt: '2026-06-29T13:24:35.091Z'
---

## Overview

js-toml is a TOML parser for JavaScript, Prior to version 1.1.2, the interpreter checks whether a key already exists in a parser-built container with `if (object[key])` instead of `if (key in object)`. When the prior value is a falsy primitive — `false`, `0`, `0n`, `0.0`, `-0`, or `""` — the duplicate-key branch is skipped and the value is silently overwritten by a later sub-table, dotted-key sub-table, or array-of-tables sharing the same name. Per the TOML 1.0.0 spec ("Defining a key multiple times is invalid"; "You cannot define any key or table more than once"), this should be a parse error. The result is structural type confusion of attacker-named keys in the value returned by `load()`. A boolean-typed `false` (or numeric `0`) becomes a truthy object. Host applications that gate behavior on `if (config.flag)`, `if (!user.banned)`, `if (config.allowDelete)`, or `if (config.publicMode)` will silently take the truthy branch. This is distinct from GHSA-65fc-cr5f-v7r2 (the 1.0.2 prototype-pollution fix). `Object.prototype` is not polluted. The `Object.create(null)` mitigation from 1.0.2 is intact; the bug here is in the duplicate-key state machine, not in container construction. Version 1.1.2 patches the incorrect comparison.

## Remediation

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

## Package advisory (CVE-2026-50029)

Affected packages:

- `js-toml <= 1.1.1`

Patched in:

- `js-toml 1.1.2`

Source: https://github.com/advisories/GHSA-m34p-749j-x6m6