A new vulnerability affect all Linux disro - How can I check if my OS (elementary OS) is affected by this so called "VPN-tunneled TCP connections." Further: How can I turn ON Reverse Path Forwarding as one of the possible mitigation solution to avoid being hihjack?
Elementary OS actual : Hera 5.1 is based on Ubutnu 18.04.
I think you talked about the vulnerability CVE-2019-14899.
after some research the vulnerability does not affect the version of Ubuntu released before version 19.10, you have more information here :