This recall affects the Crosstrek, Impreza and Forester, with model years varying from 2008 to 2017. The recall is VIN dependent, though, because not all the vehicle lines used to build these cars used the part at the center of the recall.
The issue stems from the brake light switch, a component behind the brake pedal that regulates the use of the brake lights on the vehicle's rear. Use of silicone-based consumer products, such as cleaning products or lubricants, near the brake pedal may cause that material to seep into the brake light switch housing. If that happens, it could deposit a layer of film on the switch that prevents the brake lights from turning on when the pedal is depressed.
It's important to note that if the switch is covered in a silicone film, it only affects the brake lights. It does not affect the brakes themselves -- pushing the pedal will still stop the vehicle as intended. However, without functioning brake lights, the risk of a rear-end crash may increase.
Subaru itself discovered the issue. In an email, a spokesperson for Subaru contends that it has only received "approximately 20 reports" of issues from owners. Given that low incident rate, it's likely that not many other owners have experienced this problem, but nevertheless, functional brake lights are sort of necessary.
Owners will be notified at a future date via first-class mail. To remedy the issue, Subaru's technicians will replace the brake light switch. In the meantime, don't spray a bunch of junk near your brake pedal.