Arrgh, what else? Always something: https://www.theregister.co.uk/2018/10/26/systemd_dhcpv6_rce/ Bump City ?
Come to think of it, I can't recall the Update Manager in Mint ever giving me any update titled "security."
Shades of "colour me surprised" and "I told you so"... As for me with my perfectly reliable OpenRC system, with no IPv6 in the kernel at all (don't need it yet), no action required.
Here is a Terminal tutorial on how to disable IPV6 in Debian, Ubuntu & Mint https://www.itzgeek.com/how-tos/linux/debian/how-to-disable-ipv6-on-debian-9-ubuntu-16-04.html
No problem, I haven't actually tried this myself. Normally I go into Network Manager and set IPV6 to "ignore" but that doesn't necessarily mean IPV6 is disabled.
This fix isn't supported by my older version of Mint. That's fine, like many security problems I address them in the olde way. As in if I can't fix them easily I close my eyes, then blink. Voila! No more security problem! I never posted this!!