The actress and rock singer is selling a quarter of the Nirvana frontman's back catalogue to disgraced US lifestyle guru Martha Stewart.
Released from jail this year after five months for insider trading, Stewart wants the songs as an investment.
A friend said: "It's an astonishing deal. It sorts out Courtney financially."
Cobain and Courtney, 41, wed in 1992. They had a daughter Frances Bean, now 11, before he killed himself with a gun in April 1994, aged 27.
Cobain rose to fame with songs like Smells Like Teen Spirit and Come As You Are. The album Nevermind sold over 10 million copies.