---
cve: "CVE-2021-21321"
severity: "CRITICAL"
cvss: 10.0
epss: "1.8%"
vendor: "fastify"
kev: false
exploited: false
published: "2021-03-02 04:15:12"
tags: [cve, security, critical]
source: tsecurity.de CVE-Dossier
exported: "2026-09-06T12:00:21+02:00"
---

# CVE-2021-21321

> 10.0 CRITICAL · 🧪 PoC

## Beschreibung

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.

## CVSS-Vektor

```
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
```

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Netzwerk | bad |
| AC Komplexität | Gering | bad |
| PR Privilegien | Keine | bad |
| UI Interaktion | Keine | bad |
| S Scope | Verändert | bad |
| C Vertraulichkeit | Hoch | bad |
| I Integrität | Hoch | bad |
| A Verfügbarkeit | Keine | good |

## Patch verfügbar (OSV)

- e158d9b1dec30ba130c4db7aedb047024f8dbeea (Commit)
- dea227dda606900cc01870d08541b4dcc69d3889 (Commit)

## Referenzen

- <https://github.com/fastify/fastify-reply-from/security/advisories/GHSA-qmw8-3v4g-gwj4>
- <https://www.npmjs.com/package/fastify-reply-from>
- <https://github.com/fastify/fastify-reply-from/commit/dea227dda606900cc01870d08541b4dcc69d3889>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2021-21321) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_