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.
beschreibt (1)
Zugehörige CVEs.
| ID | Schweregrad | ausnutzbar | ||
|---|---|---|---|---|
| CVE-2026-77063US | — | — | ||
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… | ||||
Referenzen
Externe Belege — Patches, Meldungen, Analysen.
- https://cna.openjsf.org/security-advisories.htmlWEB
- https://github.com/expressjs/multerPACKAGE
- https://github.com/expressjs/multer/commit/ab6aeae650328cf31799dcfa4c3e116ba8faaaccWEB
- https://github.com/expressjs/multer/releases/tag/v2.3.0WEB
- https://github.com/expressjs/multer/security/advisories/GHSA-qvfw-j98x-7q72WEB
- https://nvd.nist.gov/vuln/detail/CVE-2026-77063ADVISORY
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