multer vulnerable to Denial of Service via oversized array index in field names

Exploitation

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

CVSS

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

EPSS

• CVE-2026-82333: 0.37% estimated exploitation activity in the next 30 days; percentile 30.60 (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.

Impact multer is vulnerable to a Denial of Service (DoS) via a crafted array index in multipart field names. The append-field dependency parses bracket notation in field names, and a large numeric index such as items[4294967294] forces allocation of a maximum-length sparse array. A following field with a non-numeric key on the same base then converts that array to an object by iterating its full length, which consumes CPU synchronously and leaves the process unable to handle other requests. A single HTTP request with a crafted multipart body is sufficient to exploit this, and it affects multer 1.x and 2.x. Patches Users should upgrade to 2.3.0 and configure limits.fieldArrayIndexLimit to the minimum array index their application requires. Workarounds None.

Published by the source

8 Sep 2026, 21:28 UTC

Last modified by the source

8 Sep 2026, 21:45 UTC

Source last checked

26 Oct 2026, 13:02 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-535w-7cp7-47q4

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-535w-7cp7-47q4

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-535w-7cp7-47q4

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# Patch Next advisory brief: CVE-2026-82333

Advisory: multer vulnerable to Denial of Service via oversized array index in field names
IDs: CVE-2026-82333, GHSA-535w-7cp7-47q4
Record: https://patchnext.com/advisories/cve-2026-82333 (revision 3, source checked 26 Oct 2026, 13:02 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: multer 2.3.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm multer: affected < 2.3.0; fixed in 2.3.0

## Suggested inspection (read-only)
- `npm ls multer --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 multer.
- 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://github.com/advisories/GHSA-535w-7cp7-47q4 (GitHub-reviewed advisory GHSA-535w-7cp7-47q4 lists affected ranges: npm multer >=0 <2.3.0)
- Verified: https://osv.dev/vulnerability/GHSA-535w-7cp7-47q4 (OSV record GHSA-535w-7cp7-47q4 lists affected ranges: npm multer >=0 <2.3.0 (fixed))

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