An elderly woman had a narrow escape from her burning home after a lighted firework was pushed through the letterbox in her front door.
The 81-year-old widow heard a noise at the door of her home in Widgeon Road, Darlington, and went downstairs.
She was confronted by a wall of flames across her hallway, but managed to escape through the back door.
Durham Police said the Monday night attack was "stupid and irresponsible", and appealed for witnesses.
The woman was getting ready for bed when she heard a noise at the door.
Sparks from the firework had ignited a heavy curtain on the inside of the door and spread to carpet and wallpaper, causing considerable damage.
A roman candle firework was recovered from the scene and police said there were unconfirmed reports of up to four youths running from the scene.
Det Sgt Jeff Pow said: "This lady has had a very narrow escape as fortunately she was still getting ready for bed.
"Had she been asleep, the consequences would have been far more serious.
"This was a stupid and irresponsible thing to do and I hope we do not have to deal with any more incidents like this over the next few days."