FreeRDP before 3.32.0 contains a divide-by-zero vulnerability in the freerdp-shadow-cli shadow server: the frame id in a client's Frame Acknowledge PDU is stored without a range check, so the in-flight frame count in shadow_encoder_inflight_frames() can underflow. An authenticated client can acknowledge a frame id one greater than the last frame sent, causing shadow_encoder_create_frame_id() to divide by zero (SIGFPE) and terminate the process, disconnecting all viewers.