low3.7
CVE-2026-77063
multer vulnerable to file size limit bypass via async fileFilter race condition
Impact
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.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| npm | multer | < 2.3.0 | 2.3.0 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Expressjs | Multer | before 2.3.0 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-qvfw-j98x-7q72
- https://github.com/expressjs/multer/security/advisories/GHSA-qvfw-j98x-7q72
- https://nvd.nist.gov/vuln/detail/CVE-2026-77063
- https://github.com/expressjs/multer/commit/ab6aeae650328cf31799dcfa4c3e116ba8faaacc
- https://cna.openjsf.org/security-advisories.html
- https://github.com/expressjs/multer/releases/tag/v2.3.0