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.

CVE-2026-77078 affects multer, a Node.js middleware for handling multipart/form-data. A specially crafted multipart request with two malicious text field names can trigger an uncaught RangeError (Invalid array length), crashing the Node.js process. The attack works by using a very large numeric array index in the first field to allocate a maximum-length sparse array, then pushing past that length with a second field, causing an unhandled exception inside the append-field dependency. This is a remotely triggerable denial-of-service vulnerability requiring no authentication. All multer versions before 2.3.0 are affected. The vulnerability has been patched in multer version 2.3.0, and users are advised to upgrade immediately.