form-data-objectizer: Prototype pollution in form-data-objectizer via bracket-notation form keys

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-46510: 0.28% estimated exploitation activity in the next 30 days; percentile 20.81 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary form-data-objectizer walks bracket-notation form keys (e.g. name[sub]) into nested objects without filtering proto, constructor, or prototype. A single HTTP form field whose name starts with proto[...] causes the library to mutate Object.prototype, which is a prototype pollution primitive of the entire Node.js process. The bug is in treatInitial and treatSecond inside index.cjs: With the form key proto[polluted] and value yes: 1. treatInitial matches inputName = "proto", rest = "[polluted]". 2. "proto" in result is true (inherited), so newResult = result["proto"], which is Object.prototype. 3. treatSecond recurses with key = "polluted", newRest = "", and assigns Object.prototype.polluted = "yes". Affected versions - form-data-objectizer <= 1.0.0 (currently the only published version) Patched Not yet. Suggested fix: reject any segment equal to proto, constructor, or prototype before walking into result[inputName] / result[key]. Either throw or skip the entry. Minimum patch in…

Published by the source

18 May 2026, 13:28 UTC

Last modified by the source

9 Jun 2026, 10:45 UTC

Source last checked

26 Oct 2026, 12:53 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-m2hg-wjq3-28wq

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-m2hg-wjq3-28wq

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# Patch Next advisory brief: CVE-2026-46510

Advisory: form-data-objectizer: Prototype pollution in form-data-objectizer via bracket-notation form keys
IDs: CVE-2026-46510, GHSA-m2hg-wjq3-28wq
Record: https://patchnext.com/advisories/cve-2026-46510 (revision 2, source checked 26 Oct 2026, 12:53 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: form-data-objectizer 1.0.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm form-data-objectizer: affected <= 1.0.0; fixed in 1.0.1

## Suggested inspection (read-only)
- `npm ls form-data-objectizer --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 form-data-objectizer.
- 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-m2hg-wjq3-28wq (OSV record GHSA-m2hg-wjq3-28wq lists affected ranges: npm form-data-objectizer >=0 <1.0.1 (fixed))
- Verified: https://github.com/advisories/GHSA-m2hg-wjq3-28wq (GitHub-reviewed advisory GHSA-m2hg-wjq3-28wq lists affected ranges: npm form-data-objectizer >=0 <=1.0.0)

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