Mitigating SSRF and DNS Rebinding Attacks in Modern Web Architectures

Web features that accept user-supplied URLs for previews, web scraping, or link shortening are always vulnerable to Server-Side Request Forgery (SSRF). An attacker can force an internal server to contact cloud metadata, internal management ports, or a local database.

DNS rebinding makes this threat worse by exploiting the time gap between the IP address check (resolve time) and the moment the actual HTTP request is sent (request time). A server that only validates the domain up front can be fooled when the attacker's DNS server changes its response to a private IP such as 127.0.0.1.

Solid defenses require explicit IP resolution, verification of RFC 1918 CIDR ranges and loopback, and pinning the connection directly to the verified IP with an adjusted Host header. Blocking non-HTTP protocols and ports other than 80/443 is the core foundation of security.

Layered defenses at both the network level and in application code are the only way to keep infrastructure safe from internal infiltration.