A dog walker was grabbed by a man who pulled her towards him and repeatedly asked her for a kiss in Wellingborough.
Detectives have opened an investigation after the shocking sex assault on Friday morning (May 6).
The woman was walking her dog in a green area off Kingsway between 10am and 10.10am when the man approached her and assaulted her.
A police spokesman said: “The offender is described as white with a light tan complexion in his late 20s to early 30s, about 5ft 2in, of an average build with dark brown hair styled to the side.
"He was wearing blue jeans and a dark-coloured long sleeve top with a large logo on the front.
“A couple came to the aid of the woman and officers would like to speak to them as a matter of urgency, or anyone who witnessed what happened.”
Anyone with information should call Northamptonshire Police on 101 or Crimestoppers anonymously on 0800 555111.