Vulnerability in fastify-reply-from (CVE-2021-21321)
Summary
Vulnerability in fastify-reply-from (CVE-2021-21321). Successful exploitation can lead to full system takeover. Mitigation: upgrade to 4.0.2 or later.
Original description
The description as published by the source.
fastify-reply-from is an npm package which is a fastify plugin to forward the current http request to another server. In fastify-reply-from before version 4.0.2, by crafting a specific URL, it is possible to escape the prefix of the proxied backend service. If the base url of the proxied server is "/pub/", a user expect that accessing "/priv" on the target service would not be possible. In affected versions, it is possible. This is fixed in version 4.0.2.
Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV
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-2021-21321 has been found in fastify-reply-from.
Successful exploitation can lead to full system takeover.
What to do: upgrade fastify-reply-from to 4.0.2 or later.
If unsure, ask your IT team or search "fastify-reply-from CVE-2021-21321" on the vendor's site.
CVE-2021-21321 (fastify-reply-from) — CWE-20
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 4.0.2 — 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-20) exists in fastify-reply-from.
Check the vendor advisory for the affected versions of fastify-reply-from.
Severity: ?. Successful exploitation can lead to full system takeover.
Update to 4.0.2.
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-reply-from' . 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-reply-from' . | 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-reply-from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-reply-from to 4.0.2ステージング環境で 4.0.2 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。
-
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 github.com
- advisory nvd.nist.gov
- advisory npmjs.com
- patch github.com