Skip to content
Patch Next
Sign inAdd to your agent

← Actionable
Medium, CVSS 5.3amended

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

CVE-2026-50029GHSA-m34p-749j-x6m6

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (js-toml 1.1.2), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

Add to your agent

Affected packages

  • npm js-toml

    Affected
    <= 1.1.1
    Fixed in
    1.1.2

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
5.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
EPSS
  • CVE-2026-50029: 0.40% estimated exploitation activity in the next 30 days; percentile 34.10 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

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)…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-m34p-749j-x6m6

  2. Revision 1 · created ·

    Published from osv record GHSA-m34p-749j-x6m6

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-50029

Advisory: js-toml has silent type confusion via falsy-primitive duplicate-key bypass
IDs: CVE-2026-50029, GHSA-m34p-749j-x6m6
Record: https://patchnext.com/advisories/cve-2026-50029 (revision 2, source checked 26 Oct 2026, 12:57 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: js-toml 1.1.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm js-toml: affected <= 1.1.1; fixed in 1.1.2

## Suggested inspection (read-only)
- `npm ls js-toml --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on js-toml.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-m34p-749j-x6m6 (OSV record GHSA-m34p-749j-x6m6 lists affected ranges: npm js-toml >=0 <1.1.2 (fixed))
- Verified: https://github.com/advisories/GHSA-m34p-749j-x6m6 (GitHub-reviewed advisory GHSA-m34p-749j-x6m6 lists affected ranges: npm js-toml >=0 <=1.1.1)

Commands are suggestions: review each one before running it.

Loading voting…