Vulnerability in @fastify/busboy (CVE-2026-19481)
Summary
Vulnerability in @fastify/busboy (CVE-2026-19481). Risk of unauthorized operations or information disclosure. Exploitable via __proto__. Mitigation: upgrade to 3.2.1 or later.
Original description
The description as published by the source.
Impact
Versions of @fastify/busboy from 1.0.0 and prior to 3.2.1 are vulnerable to a Denial of Service. The multipart header parser stores part-header names on a plain JavaScript object, so a part header named __proto__ or constructor resolves to an inherited value that is not an array, and the parser throws TypeError: this.header[h].push is not a function. Through the documented req.pipe(busboy) integration this surfaces as an error event, while direct write()/end() usage throws synchronously and can terminate the Node.js process if uncaught. The parser runs before application middleware, so any unauthenticated client that can submit multipart/form-data is affected.
Patches
Fixed in version 3.2.1.
Workarounds
Attach an error listener to the Busboy stream so the parser failure is handled rather than crashing the process, and wrap direct write()/end() calls in a try/catch. Upgrading to 3.2.1 removes the failure entirely.
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-2026-19481 has been found in @fastify/busboy.
Attackers can target a specific entry point like __proto__ over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade @fastify/busboy to 3.2.1 or later.
If unsure, ask your IT team or search "@fastify/busboy CVE-2026-19481" on the vendor's site.
CVE-2026-19481 (@fastify/busboy) — CWE-754 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: __proto__ / constructor / error
Patched: 3.2.1 — apply immediately
Workaround: Attach an error listener to the Busboy stream so the parser failure is handled rather than crashing the process, and wrap direct write()/end() calls in a try/catch.
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-754) exists in @fastify/busboy. Attackers reach the vulnerable code path via __proto__ without authentication.
Check the vendor advisory for the affected versions of @fastify/busboy. Attack surface: __proto__ / constructor / error.
Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.
Update to 3.2.1.
Workaround: Attach an error listener to the Busboy stream so the parser failure is handled rather than crashing the process, and wrap direct write()/end() calls in a try/catch.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r '@fastify/busboy' . 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 '@fastify/busboy' . | 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
@fastify/busboy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
Attach an `error` listener to the Busboy stream so the parser failure is handled rather than crashing the process, and wrap direct `write()`/`end()` calls in a try/catch.パッチが適用されるまでの応急処置として、Attach an
errorlistener to the Busboy stream so the parser failure is handled rather than crashing the process, and wrap directwrite()/end()calls in a try/catch. 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 @fastify/busboy to 3.2.1ステージング環境で 3.2.1 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
- web cna.openjsf.org
- web github.com
- web nvd.nist.gov
- web github.com
- web github.com
- web github.com