Simone Margitelli's post on the find

Margitelli posted a screenshot that implies he submit this bug to Canonical and Red Hat, who rated the vulnerability to have a CVSS of 9.9. If this is true, this bug would be more critical than the infamous Heartbleed, Spectre, and Meltdown exploits. Information is really limited right now about this bug, and also somewhat contradictory. I cannot find a public statement from Red Hat or Canonical confirming the existance of this bug, but have yet to deny it. This is typical for an exploit of this magnitude. However, according to Security Online, both insitutions have confirmed its severity.

Full disclaimer, this thing could be totally overhyped/overblown right now. Its going to take a few weeks before all the information comes out. It wouldn't be the first time a vulnerability has been overhyped to pressure the dev into fixing it. In the mean time, Linux users should make sure to keep their systems up to date.