Police are appealing for information after a woman fought off an attacker in Loughton.
At around 1am on Sunday morning a woman in her 20s was walking in Barrington Road, Loughton, when she was approached from behind.
The man tried to pull her to the ground but the victim screamed and fought back.
DS Steve Jones said that no description of the man could be given.
He said: "The man assaulted the woman from behind and because he was wearing a hooded top she was not able to describe him.
"He said nothing and ran off as soon as the woman screamed.
"We want to hear from anyone who was in the area at the time and might have seen someone hanging around the area or running away.”
Anyone with information should contact DS Jones or DC Stephen Baker at Loughton CID on 101 on call Crimestoppers anonymously on 0800 555111.
Additional patrols are being carried out in the area and women walking alone have been advised to be on their guard.
Advice issued includes avoiding "badly lit alleyways" and isolated areas.
A spokesman said: "Try to use well-lit, busy streets and use the route you know best.
"Avoid passing stationary cars with their engines running and people sitting in them.
"Beware of someone who warns you of the danger of walking alone and then offers to accompany you. This is a ploy some attackers have been known to use."
There is currently no street lighting in around 70 percent of Epping Forest between 1am and 6am.