CVE-2026-82333
multer vulnerable to Denial of Service via oversized array index in field names
Impact
multer is a middleware for handling multipart/form-data in Node.js. A small multipart request with two specially crafted text field names can make multer's field parser synchronously iterate a maximum-length sparse array, blocking the event loop so the process cannot handle other requests. A large numeric array index in the first field allocates a maximum-length sparse array, and a second field with a non-numeric key then triggers a full-length iteration inside the append-field dependency. All versions before 2.3.0 are affected, and this is a remotely triggerable denial of service. multer 2.3.0 adds an opt-in fieldArrayIndexLimit option that rejects oversized array indexes. Upgrade to multer 2.3.0 and set limits.fieldArrayIndexLimit to the largest array index your application needs to remediate.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| npm | multer | < 2.3.0 | 2.3.0 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Expressjs | Multer | before 2.3.0 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-535w-7cp7-47q4
- 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/releases/tag/v2.3.0