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High, CVSS 8.2amended

parse-nested-form-data has Prototype Pollution via __proto__ in FormData field names

CVE-2026-45302GHSA-xp7r-j8r6-j9h3

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (parse-nested-form-data 1.0.1), 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.

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Affected packages

Sources

Severity and exploitation
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-2026-45302: 0.32% estimated exploitation activity in the next 30 days; percentile 24.50 (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 parseFormData() walks bracket and dot-notation FormData field names into nested objects without filtering reserved property keys. A single FormData field whose name begins with proto, or contains .proto. mid-path, causes the parser to traverse onto Object.prototype and assign properties there, polluting the prototype chain of every plain object in the running process. Details The vulnerability is in handlePathPart in src/index.ts, which performs currentObject[pathPart.path] and currentObject[pathPart.path] = val for object-type path segments without rejecting reserved keys. When the segment is proto, the read returns Object.prototype, which then becomes the next traversal target, and the next assignment lands on the prototype. Reproduction on a fresh install of parse-nested-form-data@1.0.0: Equivalent vectors: - proto[polluted]=yes - a.proto.polluted=yes (mid-path traversal) - a[0].proto.polluted=yes (mid-path through an array element) constructor.prototype.x was incidentally…

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

    Amended from ghsa record GHSA-xp7r-j8r6-j9h3

  2. Revision 1 · created ·

    Published from osv record GHSA-xp7r-j8r6-j9h3

Agent brief

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# Patch Next advisory brief: CVE-2026-45302

Advisory: parse-nested-form-data has Prototype Pollution via `__proto__` in FormData field names
IDs: CVE-2026-45302, GHSA-xp7r-j8r6-j9h3
Record: https://patchnext.com/advisories/cve-2026-45302 (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: parse-nested-form-data 1.0.1. A vendor fix does not mean a deployment is fixed.

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

## Suggested inspection (read-only)
- `npm ls parse-nested-form-data --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 parse-nested-form-data.
- 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-xp7r-j8r6-j9h3 (OSV record GHSA-xp7r-j8r6-j9h3 lists affected ranges: npm parse-nested-form-data >=0 <1.0.1 (fixed))
- Verified: https://github.com/advisories/GHSA-xp7r-j8r6-j9h3 (GitHub-reviewed advisory GHSA-xp7r-j8r6-j9h3 lists affected ranges: npm parse-nested-form-data >=0 <=1.0.0)

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