CVE-2026-5079: Expressjs Multer

High severity, CVSS 7.5. EPSS: 0.5% chance of exploitation in the next 30 days.

Impact: multer versions 1.0.0 through 2.1.1 and 3.0.0-alpha.1 are vulnerable to a Denial of Service via deeply nested field names in multipart form data. The append-field dependency parses bracket notation in field names with no limit on nesting depth, allowing an attacker to force allocation of deeply nested object structures that consume CPU and memory. A single HTTP request with a crafted multipart body is sufficient to exploit this. Patches: Users should upgrade to multer 2.2.0 (2.x line) or 3.0.0-alpha.2 (3.x prerelease) and configure the new limits.fieldNestingDepth option to the minimum depth their application requires. Workarounds: Set limits.fields to a reasonable value to reduce the number of fields an attacker can send per request. This does not fully mitigate the issue but limits the impact.

Affected products

• Expressjs Multer: from 1.0.0, before 2.2.0 (fixed in 2.2.0); version 3.0.0 only

Published 2026-06-15. Last modified 2026-06-17.