Vulnerability in Linux based VPN connections

I was browsing this Dutch tech website and stumbled on this article (in dutch)

Researchers have found a vulnerability in Linux and Unix-based operating systems that make it possible to hijack vpn connections and inject random code into data traffic.

This is probably also valid for NethServer VPN connections…
https://seclists.org/oss-sec/2019/q4/122

The author says that CentOS is NOT vulnerable, so NethServer is NOT vulnerable, too.
You can see that rp_filter is set to 0 in NethServer.

There is still a but:

I orignally listed CentOS as being vulnerable
to the attack, but this was incorrect, at least regarding IPv4. We
didn’t know the attack worked against IPv6 at the time we tested
CentOS, and I haven’t been able to test it yet.