CVE-2026-50029 js-toml has silent type confusion via falsy-primitive duplicate-key bypass
Attackers can bypass security checks in applications using js-toml by exploiting a duplicate-key parsing flaw that converts falsy values into truthy objects.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-50029?
CVE-2026-50029 is a medium-severity vulnerability in sunnyadn js-toml, published on 14 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-697
Which versions are affected by CVE-2026-50029?
2 open source packages ship an affected version, including js-toml.
| Package | Affected | Fixed in |
|---|---|---|
js-toml npm | All versions | 1.1.2 |
js-toml npm | All versions | 1.1.2 |
How do I fix CVE-2026-50029?
Upgrade js-toml to 1.1.2 or later.
Is CVE-2026-50029 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-50029 exists.
Sources
Also known as GHSA-m34p-749j-x6m6.