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CVE-2026-50029

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

CVSS 3.1 5.3 MEDIUMEUVD CVSS 3.1 5.3 CVSS 3.1 · [email protected] · Secondary 5.3 MEDIUMCVSS_V3 Publisher rating MODERATEFixed by js-toml 1.1.2KEV status unknown
Original advisory

cve-program · CVE-2026-50029

Published

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.

Read the publisher's advisory

euvd · EUVD-2026-58791

Published

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.

Read the publisher's advisory

nvd · CVE-2026-50029

Published

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.

Read the publisher's advisory

osv · GHSA-m34p-749j-x6m6

Published

### 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](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. ### Details Two truthy checks are wrong: `src/load/interpreter.ts:214` — `Interpreter.tryCreatingObject` ```js 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` ```js 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 ```toml isAdmin = false [isAdmin] forced = "yes" ``` ```js 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` ```diff export class Interpreter extends BaseCstVisitor { ignoreImplicitDeclared, ignoreExplicitDeclared ) { - if (object[key]) { + if (key in object) { if ( !isPlainObject(object[key]) || (!ignoreExplicitDeclared && ``` ```diff 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] || []; ```

Read the publisher's advisory

Affected versions, risk and source history

Exploitation and risk

Source status

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cve-program · CVE-2026-50029

Published

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

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.

Source published
14 Aug 2026 19:08:54 UTC
Source modified
17 Aug 2026 19:34:15 UTC
Saved here
23 Oct 2026 15:48:27 UTC
Source terms
CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

Source: cve-program · CVE Program Terms of Use. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 3.1 · 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

euvd · EUVD-2026-58791

Published

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 primit…

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.

Additional publisher context

EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON.

Original publisher date fields

datePublished: Aug 14, 2026, 7:08:54 PM

dateUpdated: Aug 17, 2026, 7:34:15 PM

Source published
Aug 14, 2026, 7:08:54 PM (timezone not stated)
Source modified
Aug 17, 2026, 7:34:15 PM (timezone not stated)
Saved here
11 Nov 2026 13:05:41 UTC
Source terms
ENISA EUVD · source terms and attribution apply

Original source record · Cite this exact observation · Complete original publisher JSON

Source: euvd · ENISA EUVD · source terms and attribution apply. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

EUVD CVSS 3.1 · 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

nvd · CVE-2026-50029

Published

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 primit…

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.

Additional publisher context

NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON.

Source analysis status: Deferred

Weakness classifications: CWE-697

Original publisher date fields

published: 2026-08-14T19:17:18.980

lastModified: 2026-09-18T20:09:01.757

Source published
14 Aug 2026 19:17:18 UTC
Source modified
18 Sep 2026 20:09:01 UTC
Saved here
25 Oct 2026 12:17:38 UTC
Source terms
NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

Source: nvd · NIST NVD usage terms; underlying source attribution retained. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 3.1 · [email protected] · Secondary · 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

osv · GHSA-m34p-749j-x6m6

Published

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

### 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](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. ### Details Two truthy checks are wrong: `src/load/interpreter.ts:214` — `Interpreter.tryCreatingObject` ```js 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` ```js 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 ```toml isAdmin = false [isAdmin] forced = "yes" ``` ```js 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` ```diff export class Interpreter extends BaseCstVisitor { ignoreImplicitDeclared, ignoreExplicitDeclared ) { - if (object[key]) { + if (key in object) { if ( !isPlainObject(object[key]) || (!ignoreExplicitDeclared && ``` ```diff 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] || []; ```

Source published
26 Jun 2026 22:49:28 UTC
Source modified
21 Jul 2026 17:30:26 UTC
Saved here
24 Oct 2026 13:17:17 UTC
Source terms
GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

Source: osv · GitHub Advisory Database · CC-BY-4.0. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Publisher rating · MODERATE

ChangeIntel

An IT change radar: releases, security, known issues, retirements, documentation changes, and service status from public sources. Every item links to supporting evidence; dates and statuses can change after they are read.

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