CVE-2026-107318

@fastify/reply-from is a Fastify plugin that forwards requests to an upstream HTTP or HTTPS server. In versions prior to 12.7.0, all of the built-in HTTPS transports override the secure default and set rejectUnauthorized to false, so the proxy does not verify the TLS certificate of the upstream even when the application points it at an https upstream in the default configuration. An on-path network attacker can therefore impersonate the configured HTTPS upstream, read the credentials and request bodies the proxy forwards, and return forged responses that the application trusts. The issue is fixed in @fastify/reply-from 12.7.0, and users should upgrade to 12.7.0 or later. As a workaround, pass an explicit rejectUnauthorized true on the transport, supply an already configured undici instance, or use the undici global agent.

An on-path network attacker can intercept credentials and request bodies, and return forged responses, leading to a breach of communication confidentiality and integrity. This could result in unauthorized access to upstream systems.

Update @fastify/reply-from to version 12.7.0 or later. If updating is not possible, apply the workaround: set rejectUnauthorized to true on the transport, use a configured undici instance, or use the undici global agent.