Executive brief
Multer is a widely-used Node.js middleware that handles file uploads via web forms. When uploads are aborted mid-transfer on systems using disk storage, orphaned temporary files are left behind on disk. An attacker can repeatedly initiate and abort uploads to accumulate these orphaned files, eventually exhausting available disk space and causing the application to become unavailable.
Technical details
The vulnerability is an incomplete fix for an earlier flaw: multer's diskStorage only cleans up in-flight uploads that have already been assigned a file path. When an upload is aborted before the storage engine assigns the path—particularly with asynchronous destination or filename functions—the uploaded file is written to disk with no removal mechanism in place, and the application cannot clean it up. An unauthenticated network attacker can exploit this by sending repeated multipart/form-data requests and aborting them to accumulate orphaned files in the upload directory or shared temporary directory until disk space is exhausted. The issue affects multer versions 2.2.0 through 2.3.0 and is resolved in version 2.4.0.
Affected products
- Express.js multer 2.2.0 through 2.3.0
Timeline
- 2026-09-14: disclosed: CVE-2026-88932 published
- 2026-09-14: patched: Fixed in multer 2.4.0