It appears to be an antiquated framework framework that predates any considerations regarding safety:

The vulnerability relates to the communication protocol employed in a train network referred to as the End-of-Train and Head-of-Train. A Flashing Rear End Device (FRED), commonly known as an End-of-Train (EOT) apparatus, is affixed to the rear of a train and transmits information through radio signals to a corresponding mechanism in the locomotive termed the Head-of-Train (HOT). Instructions can also be dispatched to the FRED to engage the brakes at the train’s rear.

These devices were initially deployed in the 1980s to substitute caboose cars, and regrettably, they are devoid of encryption and verification protocols. Instead, the prevailing system employs data packets exchanged between the front and rear of a train that contain a basic BCH checksum to identify errors or disruptions. However, the CISA is now alerting that an individual utilizing a software-defined radio might potentially transmit counterfeit data packets and disrupt train operations.