If they use the upstream kernel, yes. Linus Torvalds has been very clear that security is not a priority.
"We have one rule in the kernel: don't break userspace. Everything else is kind of a guideline. The whole security thing? It's a guideline that we shouldn't do stupid shit. But people do stupid shit all the time and I don't get that upset." https://www.youtube.com/watch?v=1Mg5_gxNXTo#t=8m28
Imagine, Torvalds said, that terrorists exploited a flaw in the Linux kernel to cause a meltdown at a nuclear power plant, killing millions of people. “There is no way in hell the problem there is the kernel,” Torvalds said. “If you run a nuclear power plant that can kill millions of people, you don’t connect it to the Internet.” Or if you do, he continued, you build robust defenses such as firewalls and other protections beyond the operating system so that a bug in the Linux kernel is not enough to create a catastrophe. http://www.washingtonpost.com/sf/business/2015/11/05/net-of-...
And the Linux kernel has a track record for not being the world's most secure piece of software. Which is fine, it's a project he started for fun.
It's certainly possible to pay people for a kernel that they'll stand behind commercially. If you're using, say, a RHEL kernel and a bug or vulnerability is discovered that impacts you, by all means get upset at Red Hat. If you're using a Fedora kernel, though, you made the choice to use it. It's completely unfair for you to get the benefits of running a kernel you put neither time nor money into, and not also the risk of running that kernel.