Vulnerability in @fastify/middie (CVE-2026-22031)
Summary
Vulnerability in @fastify/middie (CVE-2026-22031). Confidential information can be exposed externally. Exploitable via middie. Mitigation: upgrade to 9.1.0 or later.
Original description
The description as published by the source.
Summary
A security vulnerability exists in @fastify/middie where middleware registered with a specific path prefix can be bypassed using URL-encoded characters (e.g., /%61dmin instead of /admin). While the middleware engine fails to match the encoded path and skips execution, the underlying Fastify router correctly decodes the path and matches the route handler, allowing attackers to access protected endpoints without the middleware constraints.
Details
The vulnerability is caused by how middie matches requests against registered middleware paths.
- Regex Generation: When fastify.use('/admin', ...) is called,
middieusespath-to-regexpto generate a regular expression for the path/admin. - Request Matching: For every request,
middieexecutes this regular expression againstreq.url(orreq.originalUrl). - The Flaw:
req.urlin Fastify contains the raw, undecoded path string.- The generated regex expects a decoded path (e.g.,
/admin). - If a request is sent to
/%61dmin, the regex comparison fails (/^\/admin/does not match/%61dmin). middieassumes the middleware does not apply and callsnext().
- The generated regex expects a decoded path (e.g.,
- Route Execution: The request proceeds to Fastify's internal router, which performs URL decoding. It correctly identifies
/%61dminas/adminand executes the correspond…
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-2026-22031 has been found in @fastify/middie.
Attackers can target a specific entry point like middie over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 8.4/10.
What to do: upgrade @fastify/middie to 9.1.0 or later.
If unsure, ask your IT team or search "@fastify/middie CVE-2026-22031" on the vendor's site.
CVE-2026-22031 (@fastify/middie) — CWE-177 / CVSS v3 8.4
Attack vector: remote (network-reachable) / no user interaction
Attack surface: middie / req.url / req.originalUrl / app.js
Patched: 9.1.0 — apply immediately
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-177) exists in @fastify/middie. Attackers reach the vulnerable code path via middie.
Check the vendor advisory for the affected versions of @fastify/middie. Attack surface: middie / req.url / req.originalUrl / app.js.
Severity: High (CVSS 8.4/10). Confidential information can be exposed externally.
Update to 9.1.0.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
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
-
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 patch patch
Upgrade @fastify/middie to 9.1.0ステージング環境で 9.1.0 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。
-
3Post-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 nvd.nist.gov
- package github.com
- web github.com
- web github.com
- web github.com
- web github.com