multer is a middleware for handling multipart/form-data in Node.js. In version 2.2.0, when a disk-backed upload is aborted or truncated before the write stream finishes, multer's disk storage engine removes the visible file but does not close the underlying write file descriptor, leaving a deleted but still open descriptor. A remote attacker able to reach an upload route using the built-in disk storage can send repeated aborted or malformed multipart uploads, each one leaking a file descriptor and retaining disk blocks until the process exits, which can exhaust resources and cause a denial of service. The issue is fixed in multer 2.3.0, which closes the destination write stream on abnormal source termination and defers cleanup until the stream has closed. Upgrade to multer 2.3.0 to remediate.

CVE-2026-77037 affects multer version 2.2.0, a Node.js middleware for handling multipart/form-data. When a disk-backed upload is aborted or truncated before the write stream finishes, multer's disk storage engine removes the visible file but fails to close the underlying file descriptor. This leaves a deleted but still-open file descriptor that retains disk blocks until process exit. A remote attacker can exploit this by repeatedly sending aborted or malformed multipart uploads to any upload route using built-in disk storage. Each aborted request leaks a file descriptor and disk space, eventually exhausting system resources and causing a denial of service. The vulnerability is fixed in multer 2.3.0, which properly closes the destination write stream on abnormal source termination and defers cleanup until the stream has fully closed. Users are advised to upgrade to multer 2.3.0 immediately.