{"id":"CVE-2026-77063","aliases":["GHSA-qvfw-j98x-7q72"],"url":"https://o3.security/vulnerability/CVE-2026-77063","summary":"multer vulnerable to file size limit bypass via async fileFilter race condition","details":"### Impact\n\nWhen `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.\n\n### Patches\n\nUsers should upgrade to `2.3.0`.\n\n### Workarounds\n\nUse a synchronous `fileFilter`, or validate the uploaded file size after the upload completes.","published":"2026-08-28T19:54:58.473Z","modified":"2026-10-21T02:59:45.886029424Z","cvss":{"score":3.7,"severity":"LOW","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"npm","name":"multer","fixedVersion":"2.3.0"}],"fix":{"url":"https://github.com/expressjs/multer/commit/ab6aeae650328cf31799dcfa4c3e116ba8faaacc","label":"expressjs/multer@ab6aeae"},"references":[{"type":"ADVISORY","url":"https://cna.openjsf.org/security-advisories.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/77xxx/CVE-2026-77063.json"},{"type":"ADVISORY","url":"https://github.com/expressjs/multer/security/advisories/GHSA-qvfw-j98x-7q72"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-77063"},{"type":"WEB","url":"https://github.com/expressjs/multer/commit/ab6aeae650328cf31799dcfa4c3e116ba8faaacc"},{"type":"PACKAGE","url":"https://github.com/expressjs/multer"},{"type":"WEB","url":"https://github.com/expressjs/multer/releases/tag/v2.3.0"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T02:59:45.886029424Z"}}