CVE-2026-77063 LOW

CVE-2026-77063: multer vulnerable to file size limit bypass via async fileFilter race condition

Vendor Multer
Product multer
Weakness CWE-362
Published August 28, 2026
Last update August 28, 2026

CVSS base score

3.7/10
Attack vector Network
Attack complexity High
Privileges required None
User interaction None
Confidentiality None
Integrity Low

CVSS vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

What the vulnerability does

01Description

multer is a middleware for handling multipart/form-data in Node.js. When an application uses an asynchronous fileFilter together with the fileSize limit, a race condition in multer's file stream handling can allow a file that exceeds the configured size limit to bypass the size-limit rejection. All versions before 2.3.0 are affected. The impact is limited because the underlying multipart parser still truncates the stream at the size limit, so this is a bypass of the limit rejection rather than uncontrolled resource consumption. The issue is fixed in multer 2.3.0. Upgrade to multer 2.3.0 to remediate.

Key dates

02Disclosure timeline

August 28, 2026 CVE published

Related vulnerabilities

04Related CVE