Vulnerability in @fastify/middie (CVE-2026-6270)
Summary
Vulnerability in @fastify/middie (CVE-2026-6270). Confidential information can be exposed externally. Mitigation: upgrade to 9.3.2 or later.
Original description
The description as published by the source.
@fastify/middie versions 9.3.1 and earlier do not register inherited middleware directly on child plugin engine instances. When a Fastify application registers authentication middleware in a parent scope and then registers child plugins with @fastify/middie, the child scope does not inherit the parent middleware. This allows unauthenticated requests to reach routes defined in child plugin scopes, bypassing authentication and authorization checks. Upgrade to @fastify/middie 9.3.2 to fix this issue. There are no workarounds.
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-2026-6270 has been found in @fastify/middie.
Confidential information can be exposed externally. CVSS score: 9.1/10.
What to do: upgrade @fastify/middie to 9.3.2 or later.
If unsure, ask your IT team or search "@fastify/middie CVE-2026-6270" on the vendor's site.
CVE-2026-6270 (@fastify/middie) — CWE-436 / CVSS v3 9.1
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 9.3.2 — apply immediately
Workaround: None.
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-436) exists in @fastify/middie.
Check the vendor advisory for the affected versions of @fastify/middie.
Severity: Critical (CVSS 9.1/10). Confidential information can be exposed externally.
Update to 9.3.2.
Workaround: None.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r '@fastify/middie' . 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
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1Identify exposure identify
grep -r '@fastify/middie' . | 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/middie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
None.パッチが適用されるまでの応急処置として、None. 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/middie to 9.3.2ステージング環境で 9.3.2 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 github.com
- advisory nvd.nist.gov
- advisory github.com
- package github.com