mod_proxy is an Apache HTTP Server module that forwards client requests to back-end systems such as application servers, APIs, or internal web services. It turns Apache into a reverse proxy or gateway, which is useful for load balancing, path-based routing, and isolating internal services from direct Internet exposure.
In security terms, mod_proxy widens the trust boundary. If proxy rules are too broad, attacker-controlled input may be relayed to internal hosts, enabling server-side request forgery, unauthorized access to internal services, or routing to unintended back ends. Misconfigurations such as open proxy behavior, weak allowlists, or unsafe URL rewriting can turn a normal deployment into a pivot point. Defenders should strictly limit which destinations can be reached, verify that only intended modules are enabled, and review proxy and rewrite rules after patching. When configured carefully, mod_proxy is a strong defense layer; when configured loosely, it becomes part of the attack surface.