Technically it is a 0-day exploit (not published and unknown) but that only works on older versions of SSH. However, the default version on RHEL, Fedora are vu

Technically it is a 0-day exploit (not published and unknown) but that only works on older versions of SSH. However, the default version on RHEL, Fedora are vulnerable. So, it is a big issue if there is no patch from your distribution (unless you use ssh from source which is not common).