The 51-year-old victim was out walking her dog when she was attacked.
Oliver Welsby, without warning, grabbed his victim across the mouth and stabbed her in the stomach in Boxhill Park on the morning of July 31st. He then fled the scene.
Investigating officer, Detective Constable Jen Gibbons of Force CID based at Abingdon police station, said: "The victim sustained serious injuries to her lower abdomen, but thankfully survived the attack. However, understandably the impact of this incident on her, and the wider community, has been huge."
Welsby, 18, of no fixed abode, pleaded guilty to one count of section 18 wounding with intent, at Oxford Crown Court on Monday (3/12).
He is due to be sentenced at the same court on 18 January next year.
Detective Constable Jen Gibbons added: "I am pleased that Welsby has pleaded guilty to the offence.
"I would like to thank all those who have helped this investigation, including members of the public who came forward and for the continued support of our community."