{"id":"CVE-2026-77063","aliases":["GHSA-qvfw-j98x-7q72"],"title":"multer vulnerable to file size limit bypass via async fileFilter race condition","summary":"multer vulnerable to file size limit bypass via async fileFilter race condition","severity":"low","cvss":3.7,"cwe":["CWE-362"],"vendor":"multer","product":"multer","ecosystem":"npm","affected":["multer < 2.3.0"],"patched":["multer 2.3.0"],"published":"2026-09-08","updated":"2026-09-08","sourceUpdated":"2026-09-08T21:29:43Z","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-qvfw-j98x-7q72","references":[{"url":"https://github.com/expressjs/multer/security/advisories/GHSA-qvfw-j98x-7q72"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-77063"},{"url":"https://github.com/expressjs/multer/commit/ab6aeae650328cf31799dcfa4c3e116ba8faaacc"},{"url":"https://cna.openjsf.org/security-advisories.html"},{"url":"https://github.com/expressjs/multer/releases/tag/v2.3.0"},{"url":"https://github.com/advisories/GHSA-qvfw-j98x-7q72"}],"tags":["ghsa","npm"],"epss":0.0016,"epssPercentile":0.05602,"ingestedAt":"2026-09-08T22:12:30.967Z","slug":"CVE-2026-77063","body":"## Overview\n\n### 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.\n\n## Affected packages\n\n- `multer < 2.3.0`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `multer 2.3.0`","depth":"sunlit","depthScore":20,"depthScoreParts":{"impact":20.4,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}