CVE-2021-21322: fastify-http-proxy: crafted URL allows prefix scape of the proxied backend service

Severity: Critical

CVSS Score: 10

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.