multer vulnerable to Denial of Service via oversized array index in field names
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.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | multer | < 2.3.0 | 2.3.0 |
References
- https://github.com/expressjs/multer/security/advisories/GHSA-535w-7cp7-47q4
- https://nvd.nist.gov/vuln/detail/CVE-2026-82333
- https://github.com/expressjs/multer/pull/1438
- https://github.com/expressjs/multer/commit/73c1759fa93b87366bc6dbd7abe1b80ddff7d27c
- https://cna.openjsf.org/security-advisories.html
- https://github.com/expressjs/multer
- https://github.com/expressjs/multer/releases/tag/v2.3.0
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-400- Platform
- npm
- Package
multer- Disclosed
- 08.09.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-535w-7cp7-47q4 - CC BY 4.0
Vulnerability history: multer
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 14
- First → latest
- 05.2025 09.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 11
- Medium 2
- Low 1
Disclosures per year
- 2025: 4
- 2026: 10
-
multer vulnerable to Denial of Service via oversized array index in field names this entry
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