They are not supposed to be harmed during the war. But ideal situations hardly happen in war times. Red cross volunteers do get killed in the cross fire and the symbol doesn't give real protection to parties that do not honor the international agreement of keeping their crosshairs away from noncombatants.
In War both combatants and Service providers and moderators like Red Cross and Crescent are prone to Injuries and Possible , being killed. Many Red Cross Officers has been killed in War Zones the world over.
Nevertheless, there is a Subsisting multilateral agreements barring combatants from intentionally harming service providers in War Zones. There is a sanction for every party complicit of this multi lateral agreement!!