Subaru of America, Inc. (Subaru) is initiating a service campaign for certain 2015-2018 Forester 2.0L Turbo and 2016-2018 WRX models which may experience a loosening of the front exhaust pipe nuts. On certain affected vehicles, the six (6) front exhaust pipe (EPF) nuts at the cylinder heads may not have been tightened sufficiently due to variations in production. As a result, these nuts may become loose during use and cause exhaust leakage. A leak occurring at the front exhaust pipe may result in deterioration of emission performance. As a result, affected vehicle may fail to meet emission levels certified by the EPA and/or California ARB.