Vulnerability in multer (CVE-2026-5079)
Summary
Vulnerability in multer (CVE-2026-5079). Risk of unauthorized operations or information disclosure. Exploitable via limits.fieldNestingDepth. Mitigation: upgrade to 3.0.0-alpha.2 or later.
Original description
The description as published by the source.
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.
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-5079 has been found in multer.
Attackers can target a specific entry point like limits.fieldNestingDepth over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade multer to 3.0.0-alpha.2 or later.
If unsure, ask your IT team or search "multer CVE-2026-5079" on the vendor's site.
CVE-2026-5079 (multer) — CWE-400 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: limits.fieldNestingDepth / limits.fields
Patched: 3.0.0-alpha.2 — apply immediately
Workaround: Set limits.fields to a reasonable value to reduce the number of fields an attacker can send per request.
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-400) exists in multer. Attackers reach the vulnerable code path via limits.fieldNestingDepth without authentication.
Check the vendor advisory for the affected versions of multer. Attack surface: limits.fieldNestingDepth / limits.fields.
Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.
Update to 3.0.0-alpha.2.
Workaround: Set limits.fields to a reasonable value to reduce the number of fields an attacker can send per request.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'multer' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'multer' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
multerを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply temporary workaround mitigate
Set `limits.fields` to a reasonable value to reduce the number of fields an attacker can send per request.パッチが適用されるまでの応急処置として、Set
limits.fieldsto a reasonable value to reduce the number of fields an attacker can send per request. を実施。回避策の副作用 (機能低下) を確認した上で。 -
3Apply patch patch
Upgrade multer to 3.0.0-alpha.2ステージング環境で 3.0.0-alpha.2 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
4Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory cna.openjsf.org
- advisory github.com
- advisory nvd.nist.gov
- advisory github.com
- package github.com
- web github.com