CVE-2026-77063

multer vulnerable to file size limit bypass via async fileFilter race condition

Published Aug 28, 2026 CVSS 3.1 · 3.7 Low EPSS < 1% KEV · Not listed
Description
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-qvfw-j98x-7q72 multer vulnerable to file size limit bypass via async fileFilter race condition
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Expressjs
Expressjs multer
CPEs cpe:2.3:a:expressjs:multer:*:*:*:*:*:node.js:*:*
Vendors & Products Expressjs
Expressjs multer
Type Values Removed Values Added
First Time appeared Multer
Multer multer
Vendors & Products Multer
Multer multer
Type Values Removed Values Added
Description 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.
Title multer vulnerable to file size limit bypass via async fileFilter race condition
Weaknesses CWE-362
References
Metrics cvssV3_1

{'score': 3.7, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
openjs
Published
Updated
Aug 31, 2026, 6:40 PM
Reserved
Aug 20, 2026, 9:59 AM
Status
Analyzed
Published
Aug 28, 2026, 10:16 PM
Modified
Sep 2, 2026, 2:46 PM