Curses can be eternal, and are carried forward generation after generation, till the cursed standing before the great white throne for final judgment. The Biblical way to break all such curses is fairly simple and easy, yet not many know about it.

Proverbs 3:33
The LORD'S curse is on the house of the wicked,
but He blesses the dwelling of the righteous.

Proverbs 26:2
Like a sparrow in its flitting, like a swallow in its flying,
a curse that is causeless does not alight.