Description
multer is a middleware for handling multipart/form-data in Node.js. A small multipart request containing two specially crafted text field names can cause an uncaught RangeError (Invalid array length) that terminates the Node.js process. The first field uses a very large numeric array index to allocate a maximum-length sparse array, and a second field then pushes past that length, which throws inside the append-field dependency and is not caught by multer. All versions before 2.3.0 are affected, and the issue is a remotely triggerable denial of service. The issue is fixed in multer 2.3.0. Upgrade to multer 2.3.0 to remediate.
Affected products
expressjs: multer
References2
- cna.openjsf.org/security-advisories.html Vendor Advisory
- github.com/expressjs/multer/security/advisories/GHSA-wc9g-mqfw-… Vendor Advisory
Metrics
- CVSS 3.1
-
7.5
HIGH
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - EPSS — exploit probability
- 0% percentile: 42 · as of 8 November 2026
- CWE
- CWE-248
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.