A forward-proxy is a server or network function that sends requests on behalf of a client. Instead of the client connecting directly to a destination, it asks the proxy to relay the traffic. Organizations use forward proxies for filtering, logging, authentication, caching, and access control, especially for outbound web traffic.
In cyber security, forward proxies matter because they can become trust boundaries. If a service unintentionally behaves like a proxy, an attacker may abuse it to reach internal or external targets that should not be reachable. This is a common pattern in server-side request forgery, where a vulnerable application is tricked into making requests for the attacker. Defenders look for unexpected proxy behavior, tight egress rules, and logs showing unusual destinations, methods, or headers. In gateway appliances, unintended forward-proxy functions can be especially risky because they sit between users and protected resources.