What’s Vulnerable › Vulnerabilities

CVE-2021-21322: Prefix escape

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-03-02 · updated 2026-06-17
• Weakness: CWE-20

Description

fastify-http-proxy is an npm package which is a fastify plugin for proxying your http requests to another server, with hooks. 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 4.3.1.

Affected products

• fastify-http-proxy: before 4.3.1 — fixed in 4.3.1

How to fix

Upgrade to a fixed version: fastify-http-proxy 4.3.1. Check the vendor advisory for mitigations.

References

• https://github.com/fastify/fastify-http-proxy/commit/02d9b43c770aa16bc44470edecfaeb7c17985016
• https://github.com/fastify/fastify-http-proxy/security/advisories/GHSA-c4qr-gmr9-v23w
• https://www.npmjs.com/package/fastify-http-proxy
• https://github.com/fastify/fastify-http-proxy/commit/02d9b43c770aa16bc44470edecfaeb7c17985016
• https://github.com/fastify/fastify-http-proxy/security/advisories/GHSA-c4qr-gmr9-v23w
• https://www.npmjs.com/package/fastify-http-proxy

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