Multer vulnerable to Denial of Service via deeply nested field names
Impact
Multer is vulnerable to a Denial of Service (DoS) via deeply nested field names in multipart form data. The append-field dependency parses bracket notation in field names (e.g., a[b][c]) 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 2.2.0 and configure limits.fieldNestingDepth 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 software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | multer | >= 1.0.0, < 2.2.0, >= 3.0.0-alpha.1, < 3.0.0-alpha.2 | 2.2.0, 3.0.0-alpha.2 |
References
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-400- Platform
- npm
- Package
multer- Disclosed
- 17.06.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-72gw-mp4g-v24j - CC BY 4.0
Vulnerability history: multer
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 14
- First → latest
- 05.2025 09.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 11
- Medium 2
- Low 1
Disclosures per year
- 2025: 4
- 2026: 10
-
Multer vulnerable to Denial of Service via deeply nested field names this entry
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