{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 1.1.1"
      },
      "package": {
        "ecosystem": "npm",
        "name": "js-toml"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.1.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-50029"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-697"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-26T22:49:28Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Summary\n\n`js-toml`\u0027s 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 \u2014 `false`, `0`, `0n`, `0.0`, `-0`, or `\"\"` \u2014 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.\n\nThe 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.\n\nThis is **distinct** from [GHSA-65fc-cr5f-v7r2](https://github.com/sunnyadn/js-toml/security/advisories/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.\n\n### Details\n\nTwo truthy checks are wrong:\n\n`src/load/interpreter.ts:214` \u2014 `Interpreter.tryCreatingObject`\n\n```js\nif (object[key]) {            // falsy primitives slip through\n    // duplicate-key logic\n} else {\n    object[key] = createSafeObject();   // silently overwrites the prior falsy value\n    ...\n}\n```\n\n`src/load/interpreter.ts:278` \u2014 `Interpreter.getOrCreateArray`\n\n```js\nif (object[first] \u0026\u0026 !Array.isArray(object[first])) {   // same flaw\n    throw new DuplicateKeyError();\n}\nobject[first] = object[first] || [];   // overwrites the prior falsy value\n```\n\nBoth should use the `in` operator. Containers are created via `Object.create(null)`, so `in` is unambiguous (no inherited keys to worry about).\n\nThe bug is reachable through every parent-walking interpreter path:\n\n- `assignValue` \u2014 dotted keys in `key = value`\n- `createTable` \u2014 `[stdTable]` headers\n- `getOrCreateArray` \u2014 `[[arrayOfTables]]` headers\n\n### PoC\n\n```toml\nisAdmin = false\n[isAdmin]\nforced = \"yes\"\n```\n\n```js\nimport { load } from \u0027js-toml\u0027;\n\nconst config = load(`\nisAdmin = false\n[isAdmin]\nforced = \"yes\"\n`);\n\nconsole.log(JSON.stringify(config));\n// {\"isAdmin\":{\"forced\":\"yes\"}}\n\nconsole.log(config.isAdmin ? \u0027BYPASS\u0027 : \u0027safe\u0027);\n// BYPASS\n\nif (config.isAdmin) {\n  // attacker reaches admin-only code\n}\n```\n\n### Impact\n\nSpec-violating input acceptance leading to structural type confusion. (CWE-697)\n\n### Suggested fix\n\nin `src/load/interpreter.ts`\n\n```diff\nexport class Interpreter extends BaseCstVisitor {\n     ignoreImplicitDeclared,\n     ignoreExplicitDeclared\n   ) {\n-    if (object[key]) {\n+    if (key in object) {\n       if (\n         !isPlainObject(object[key]) ||\n         (!ignoreExplicitDeclared \u0026\u0026\n```\n```diff\nexport class Interpreter extends BaseCstVisitor {\n       return this.getOrCreateArray(keys, object[first], idx + 1);\n     }\n\n-    if (object[first] \u0026\u0026 !Array.isArray(object[first])) {\n+    if (first in object \u0026\u0026 !Array.isArray(object[first])) {\n       throw new DuplicateKeyError();\n     }\n\n     object[first] = object[first] || [];\n```",
  "id": "GHSA-m34p-749j-x6m6",
  "modified": "2026-06-26T22:49:28Z",
  "published": "2026-06-26T22:49:28Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/sunnyadn/js-toml/security/advisories/GHSA-m34p-749j-x6m6"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/sunnyadn/js-toml"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "js-toml has silent type confusion via falsy-primitive duplicate-key bypass"
}