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Vulnerability record · CVE-2026-77063 · published 28 August 2026

CVE-2026-77063: Expressjs multer race condition vulnerability

Expressjs · Multer

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's file stream handling can allow a file that exceeds the configured size limit to bypass the size-limit rejection. All versions before 2.3.0 are affected. The impact is limited because the underlying multipart parser still truncates the stream at the size limit, so this is a bypass of the limit rejection rather than uncontrolled resource consumption. The issue is fixed in multer 2.3.0. Upgrade to multer 2.3.0 to remediate.

3.7 CVSS 3.1 Low EPSS 0.23% · top 87.2% CWE-362 · Race condition
3.7CVSS 3.1 base score
0.23%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
2References
2 Sep 2026Last modified by NVD

Description

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's file stream handling can allow a file that exceeds the configured size limit to bypass the size-limit rejection. All versions before 2.3.0 are affected. The impact is limited because the underlying multipart parser still truncates the stream at the size limit, so this is a bypass of the limit rejection rather than uncontrolled resource consumption. The issue is fixed in multer 2.3.0. Upgrade to multer 2.3.0 to remediate.

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://cna.openjsf.org/security-advisories.html Vendor Advisory
https://github.com/expressjs/multer/security/advisories/GHSA-qvfw-j98x-7q72 Vendor AdvisoryMitigation

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-77063), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.