Server-Side Request Forgery (SSRF)

When it applies

The server makes an outbound request to a destination you control or influence. Even a "blind" fetch (no response shown) is useful if you can see the callback and reach internal services.

Why it works

The request originates from inside the trust boundary, so it bypasses network ACLs and hits things you can't reach directly: cloud metadata, internal admin panels, databases, other microservices — often unauthenticated because they "only accept internal traffic".