The allegations from the woman, identified as Julie Swetnick, come on the eve of a special session of the judiciary committee, in which both Kavanaugh and another accuser, Christine Blasey Ford, will appear separately.
Swetnick's allegation was that Kavanaugh had been among a group of young men who, in high school, would spike the drinks of girls at parties before taking them into bedrooms to be "gang raped". She said she managed to flee to the bathroom when Judge jumped on her and Kavanaugh, knocking them off the bed.
Judge's name has come up so often in the various allegations against Kavanaugh and in Thursday's hearing that it beggars belief he still hasn't been called to testify.
Swetnick said that she attended more than 10 parties with Kavanaugh and Judge between 1981 and 1983.
But Mr Kavanaugh denied sexually assaulting anyone, "not in high school, not in college, never". In 2012 during a couples therapy session, he says, she revealed that in high school she had been "trapped in a room and physically restrained by one boy who was molesting her while another boy watched".
Tapper pointed out that the Federal Bureau of Investigation is not likely to investigate the allegations against Kavanaugh, and asked Avenatti if he would give CNN the names of the witnesses.
Earlier, Kavanaugh has been accused of sexual assault and misconduct by two other women.
Feinstein then asked if Kavanaugh wanted to elaborate on his comments about Swetnick's accusations.
In the face of the new allegations against Kavanaugh, the Democrats of the Senate Judiciary Committee have called on Trump to either withdraw Kavanaugh's nomination or to direct the FBI to reopen an investigation into his background. Perhaps we will learn that she is unreliable and there are reasons to disbelieve everything she says.
Kavanaugh's official response to that claim was, "This is ridiculous and from The Twilight Zone". In order to be appointed to the Supreme Court, Kavanaugh's nomination must now be confirmed by the US Senate, which the Republican Party narrowly controls 51-49. Only Kavanaugh and Ford are set to testify before the Senate committee on Thursday. "I don't know what his reputation as a lawyer is".
Swetnick told Heilemann, "Brett Kavanaugh is going for a seat where he's going to have that seat on the Supreme Court for the rest of his life". "The standard of character and fitness for a position on the nation's highest court must be higher than this".
"During the incident, I was incapacitated without my consent and unable to fight off the boys raping me", Swetnick writes, continuing on to claim that she told at least two others about the assault shortly after it happened, and that she believed she was drugged "using Quaaludes or something similar placed in what I was drinking".