要点
- CVE-2026-5079 は multer (expressjs), multer に影響する深刻度「高」 (CVSS 7.5) の脆弱性です。
- 今後30日間に悪用される確率（EPSS）：0.28%（全脆弱性の 20.4% より高い）。
- 対処：2.2.0, 3.0.0-alpha.2 以降に更新してください。
| パッケージ | 影響を受けるバージョン | 修正済みバージョン |
|---|
| multer | = 3.0.0≥ 1.0.0, < 2.2.0
| 2.2.0
|
| multer npm | ≥ 1.0.0, < 2.2.0≥ 3.0.0-alpha.1, < 3.0.0-alpha.2
| 2.2.03.0.0-alpha.2
|
概要
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.
NVD の説明
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.
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