The Hole singer says she and the supermodel had a fling in Milan, Italy, in the 90s but is adamant Kate won't care about her lesbian revelations.
She told Irish magazine Hot Press: "It was Kate Moss. She doesn't care. It'sa great story for the grandchildren, so yeah. Kate wasn't doing a lot of drugs it was just a thing that happened in Milan in the 90s.
"It happened and it was fun and whatever. And she talks about it and so I hope she doesn't get mad that I outed her about it.
"I feel like such a kiss and tell. Kate's great, though! Kate's a good friend of mine. I almost bought her house in St John's Wood, London."
Both Kate and Courtney have had tempestuous love lives.
Kate, 36, is currently dating The Kills guitarist Jamie Hince, and has previously romanced Johnny Depp and troubled singer Pete Doherty.
Courtney is best known for her marriage to Nirvana frontman Kurt Cobain, who killed himself in April 1994.
She also dated Gavin Rossdale prior to his marriage to No Doubt singer Gwen Stefani.
Discussing Gavin, she said: "Me and Gavin dated for eight months, but never when they were engaged. He was playing the field. One night Gavin made roast chicken and it was really, really good. And then we snogged and he was really good at it. He'd improved vastly from the last time we'd snogged."
She is currently in a relationship with hotelier Andre Balazs and is said to have "hit the roof" last week when he began chatting to a business partner on a night out.
A source said: "Andre was stopped by a woman he knew. As soon as he started talking to her, Courtney hit the roof. It was obvious to everyone that the woman was a business associate, but not to Courtney. She acted like a toddler!"
