The incident happened in Colne Road, Burnley between 11 and 11.30pm on July 23 and officers have issued a description of the man she fought off.
Lancashire Police said: “We need your help after a young woman was sexually assaulted on Colne Road, Burnley, between 11pm and 11.30pm on Saturday night.
“She fought off the male suspect who was white, with short strawberry blond hair and a short beard.”
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Anyone with information or dashcam footage from the area is asked to call 101.