Red snake attack in a dream can be triggered by external stimulus.
For anyone, recently in waking life encountered an intensive movement of a thing in a red color can be a source of dreaming about attack by red snake. A movement of a red car, or a bike, a burning cigarette, or a seeing of a red colored sunset can be an inspiration for your dream.
For a woman, a sudden start of a monthly period can be an external stimulus of dreaming about an attack of red colored snake.
For a man, a sharp feeling of spontaneous erection induced by blood flow into a body part is a cause for the dreams about the red long limbless reptiles attacks. And these feelings can be felt up to few times per sleep.
Also, if closed eyes suddenly being touched by red colored light rays of rising sun early in a morning, this happening can be used by our subconsciousness to build a vision of a red color snake behaving aggressively and attacking us or someone else.