multer vulnerable to file size limit bypass via async fileFilter race condition
Impact
When multer is configured with an asynchronous fileFilter, the limits.fileSize limit can be bypassed. The 'limit' event is registered inside the async fileFilter callback, so if a file exceeds limits.fileSize before that callback runs, the event is missed and the oversized upload is accepted instead of being rejected with a LIMIT_FILE_SIZE error. Applications that rely on limits.fileSize to reject oversized uploads are affected on all upload methods (.single(), .array(), .fields(), .any()). Uploads using a synchronous fileFilter are not affected.
Patches
Users should upgrade to 2.3.0.
Workarounds
Use a synchronous fileFilter, or validate the uploaded file size after the upload completes.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | multer | < 2.3.0 | 2.3.0 |
References
- 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
- https://github.com/expressjs/multer/releases/tag/v2.3.0
- CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N- Weakness (CWE)
CWE-362- Platform
- npm
- Package
multer- Disclosed
- 08.09.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-qvfw-j98x-7q72 - CC BY 4.0
Vulnerability history: multer
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 14
- First → latest
- 05.2025 09.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 11
- Medium 2
- Low 1
Disclosures per year
- 2025: 4
- 2026: 10
-
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