Nirvana and Kurt Cobain's estate are being told nevermind when it comes to the dismissal of a child pornography lawsuit centered around a famous album cover ... 'cause the lawsuit is back on.

The U.S. Court of Appeals for the Ninth Circuit revived the lawsuit Thursday, reversing a lower court's decision to toss the whole thing.

Remember ... Spencer Elden says he's the naked baby pictured on the band's "Nevermind" album cover. Of course, he's all grown up now and in 2021 he filed suit against Nirvana and Cobain's estate over the cover.

Spencer accused Nirvana of publishing child porn by using a nude photo of him on the album cover way back in 1991 ... when he was just four months old.

The suit was dismissed in September 2022 ... when a district judge in California ruled Spencer had waited too long to sue Nirvana.

Now, the appeals court says the suit can go forward because Nirvana republished the album cover in 2021 when the band re-released "Nevermind" and held that each republication of the cover may constitute a new injury to Elden ... clearing the way for Spencer to continue his lawsuit against the Seattle grunge band.