She was seriously assaulted while walking in Campsie Road, Milton Of Campsie, Dumbartonshire, at about 1.20am on Sunday.
She suffered facial injuries and police said she was traumatised after her ordeal.
The attacker was white, about 5ft 3in, with short dark hair. He was wearing a dark, waist-length jacket with the hood up. The jacket collar had grey and white spots on it and he was wearing dark jogging bottoms.