Vulnerability-Lookup

CVE-2026-50029 (GCVE-0-2026-50029)

Vulnerability from cvelistv5 – Published: 2026-08-14 19:08 – Updated: 2026-08-17 19:34

Title

js-toml has silent type confusion via falsy-primitive duplicate-key bypass

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 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.

Severity

5.3 (Medium)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

SSVC

Exploitation: poc Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-08-17 19:34 UTC

CWE

CWE-697 - Incorrect Comparison

Assigner

GitHub_M mitre root Scorecard

References

3 references

URL	Tags
https://github.com/sunnyadn/js-toml/security/advi…	x_refsource_CONFIRM
https://github.com/sunnyadn/js-toml/commit/e0504f…	x_refsource_MISC
https://github.com/sunnyadn/js-toml/releases/tag/v1.1.2	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
sunnyadn	js-toml	Affected: < 1.1.2	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-50029

Vulnerability from fkie_nvd - Published: 2026-08-14 19:17 - Updated: 2026-09-18 20:09

Severity

5.3 (Medium) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/sunnyadn/js-toml/commit/e0504fa5d3dcde2d1d588c9001c24b7b700beeeb
	security-advisories@github.com	https://github.com/sunnyadn/js-toml/releases/tag/v1.1.2
	security-advisories@github.com	https://github.com/sunnyadn/js-toml/security/advisories/GHSA-m34p-749j-x6m6
	134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/sunnyadn/js-toml/security/advisories/GHSA-m34p-749j-x6m6

Impacted products

	Vendor	Product	Version

JSON

To clipboard

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    {
      "affectedData": [
        {
          "product": "js-toml",
          "vendor": "sunnyadn",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 1.1.2"
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    }
  ],
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          "integrityImpact": "LOW",
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}

GHSA-M34P-749J-X6M6

Vulnerability from github – Published: 2026-06-26 22:49 – Updated: 2026-07-21 17:23

Summary

js-toml has silent type confusion via falsy-primitive duplicate-key bypass

Details

Summary

js-toml's 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.

Details

Two truthy checks are wrong:

src/load/interpreter.ts:214 — Interpreter.tryCreatingObject

if (object[key]) {            // falsy primitives slip through
    // duplicate-key logic
} else {
    object[key] = createSafeObject();   // silently overwrites the prior falsy value
    ...
}

src/load/interpreter.ts:278 — Interpreter.getOrCreateArray

if (object[first] && !Array.isArray(object[first])) {   // same flaw
    throw new DuplicateKeyError();
}
object[first] = object[first] || [];   // overwrites the prior falsy value

Both should use the in operator. Containers are created via Object.create(null), so in is unambiguous (no inherited keys to worry about).

The bug is reachable through every parent-walking interpreter path:

assignValue — dotted keys in key = value
createTable — [stdTable] headers
getOrCreateArray — [[arrayOfTables]] headers

PoC

isAdmin = false
[isAdmin]
forced = "yes"

import { load } from 'js-toml';

const config = load(`
isAdmin = false
[isAdmin]
forced = "yes"
`);

console.log(JSON.stringify(config));
// {"isAdmin":{"forced":"yes"}}

console.log(config.isAdmin ? 'BYPASS' : 'safe');
// BYPASS

if (config.isAdmin) {
  // attacker reaches admin-only code
}

Impact

Spec-violating input acceptance leading to structural type confusion. (CWE-697)

Suggested fix

in src/load/interpreter.ts

export class Interpreter extends BaseCstVisitor {
     ignoreImplicitDeclared,
     ignoreExplicitDeclared
   ) {
-    if (object[key]) {
+    if (key in object) {
       if (
         !isPlainObject(object[key]) ||
         (!ignoreExplicitDeclared &&

export class Interpreter extends BaseCstVisitor {
       return this.getOrCreateArray(keys, object[first], idx + 1);
     }

-    if (object[first] && !Array.isArray(object[first])) {
+    if (first in object && !Array.isArray(object[first])) {
       throw new DuplicateKeyError();
     }

     object[first] = object[first] || [];

Severity

5.3 (Medium)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Show details on source website

JSON

To clipboard

{
  "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": "2026-07-21T17:23:38Z",
  "published": "2026-06-26T22:49:28Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/sunnyadn/js-toml/security/advisories/GHSA-m34p-749j-x6m6"
    },
    {
      "type": "WEB",
      "url": "https://github.com/sunnyadn/js-toml/commit/e0504fa5d3dcde2d1d588c9001c24b7b700beeeb"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/sunnyadn/js-toml"
    },
    {
      "type": "WEB",
      "url": "https://github.com/sunnyadn/js-toml/releases/tag/v1.1.2"
    }
  ],
  "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"
}

Sightings

Author	Source	Type	Date	Other

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Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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Action not permitted

CVE-2026-50029 (GCVE-0-2026-50029)

FKIE_CVE-2026-50029

GHSA-M34P-749J-X6M6

Summary

Details

PoC

Impact

Suggested fix

Tags

Sightings

Nomenclature

Related by attack behaviour