In my screenshot below, it shows my Linux Mint 18.3 desktop with 3 pending updates. Click on it for a full-sized version. The top two are regarding the recent flaws revealed in processors with speculative processing and fix them and it also looks like they might also have code to handle the AMD issue, judging by the release notes.
Still, these are serious patches. The urgency is marked as low for them probably because there haven't been any vulnerabilities in the wild (yet), though the CVE rates this issue as Medium. But the bigger thing here is that the impact is 4. Note that the numbers used beside updates in LM isn't the priority, it's the impact on the system as a whole. And because these are kernel-related updates, things could break.
Apply them one at a time as recommended in the legend and do an image beforehand. I assume this means to apply an update and then reboot and use your computer enough to make sure it works before applying another update. With level 4 updates, I tend to just install one each day until they're all done. Timeshift, which comes with Linux Mint 18.3 is great for backing up an image, btw. But you could use Clonezilla if you prefer.
These updates are upstream from Ubuntu so other Ubuntu-derived distros should have them now, too.
This is one of the features I like about Linux Mint. Any other distro, you might apply all these patches together and not prepare an image backup beforehand and end up with an unbootable system. The impact level warns you of this.
