Not all hope is lost, however. First, this bar only applies where a specific finding of fraud has been made. Sometimes USCIS expresses that it will deny a petition because it isn't convinced about the marriage but stops short of expressly stating that it finds fraud to have occurred.
Secondly, the law requires USCIS to at least accept future applications and look at the fraud question afresh each time. In other words, they cannot simply point to the past finding of fraud and deny the new petition. The new officer has to make his or her own finding of fraud -- although that is very often just what they do.
Finally, there is a waiver available under section 237(a)(1)(H) of the Immigration and INA that can preserve an already granted green card despite the fraud, though this is difficult to win and can only be sought by someone who is already in removal proceedings.
It should go without saying that anyone with a marriage fraud finding needs the immediate help of an experienced immigration attorney before any steps are taken to preserve, replace, or obtain their green card.