A flaw was found in fastify-reply-from. Escaping of the prefix of the proxied backend service is possible allowing an attacker, using a specially crafted URL, to gain access to directories that would otherwise be out of bounds. The highest threat from this vulnerability is to data confidentiality and integrity.

Impact

The main repo of fastify use fast-content-type-parse to parse request Content-Type, which will trim after split.

The fastify-reply-from have not use this repo to unify the parse of Content-Type, which won't trim.

As a result, a reverse proxy server built with @fastify/reply-from could misinterpret the incoming body by passing an header ContentType: application/json ; charset=utf-8. This can lead to bypass of security checks.

Patches

@fastify/reply-from v9.6.0 include the fix.

Workarounds

There are no known workarounds.

References

Hackerone Report: https://hackerone.com/reports/2295770.

Summary By crafting a malicious URL, an attacker could access routes that are not allowed, even though the reply.from is defined for specific routes in @fastify/reply-from.

Details

An attacker can bypass the route defined by the @fastify/reply-from package by adding a .. symbol, which, for curl version 8.7.1, is %2e%2e.

Impact

Everyone is using this package with the routes option to protect a 3rd-party resource.