Phoronix reader Brendan tipped us off today to an interesting mailing list post earlier this month when discussing the potential of an Ubuntu MATE Remix, a version of Ubuntu Linux that would incorporate the GNOME-forked MATE desktop by default.
Ubuntu Linux developer Oliver Grawert had originally pointed out that security updates from Ubuntu don't necessarily get down to Linux Mint users since changes from X.Org, the kernel, Firefox, the boot-loader, and other core components are blocked from being automatically upgraded. Linux Mint doesn't send down updates for some Ubuntu packages automatically due to having their own customizations, etc.
The list of update rules can be found via GitHub as pointed out by Oliver in a follow-up post. Grawert explained, "this is the list of packages it will never update, instead of just integrating changes properly with the packagaes in the ubuntu archive they instead suppress doing (security) updates at all for them. i would say forcefully keeping a vulnerable kernel browser or xorg in place instead of allowing the provided security updates to be installer makes it a vulnerable system, yes. i personally wouldn't do online banking with it ;)"
Another Ubuntu developer, Benjamin Kerensa, added, "It is unclear why Linux Mint disables all of their security updates although to some degree they have tried to justify their disabling of kernel updates by suggesting that such updates could make a system unstable and that normal users shouldn't get these kinds of updates. Anyways it is something that might be better researched on their forums since people have asked a few times over the past couple years, and they probably have a better idea than us. I can say that it took them many months to get a fixed version of Firefox packaged while Ubuntu and Debian had already had security fixes in their package. This puts Linux Mint users at risk and is one of the key reasons I never suggest Linux Mint to anyone as an alternative to Ubuntu."
Update: There's a comment on the matter from the Linux Mint perspective over on their blog with their reasoning.