A coupling bushing includes a bushing body and a retainer for locking a coupling plug into the bushing body. The bushing body has a connecting section and a coupling section, wherein the connecting section and the coupling section are fluidically connected with each other via an inner channel. A bushing valve is arranged in the inner channel (8), wherein the bushing valve (10a) comprises a valve holder, an axially movable valve body and a valve seat. The retainer has at least one latching element, wherein the at least one latching element has a resiliently elastic design. The at least one latching element is designed to engage with a coupling plug.