GHSA-qvfw-j98x-7q72
multer vulnerable to file size limit bypass via async fileFilter race condition
Packages
Details
As written in the advisory (Markdown source, shown as plain text).
### 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.
References
External links from the advisory. They lead to third-party sites.
- 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