The Linux kernel is not usable as a security boundary, so anyone who wants to do "shared hosting" and not be hacked needs to use something else, like gVisor or firecracker VMs
The only important system that uses it as a security boundary is Android and there is mitigated by the fact that APKs need user approval, plus strict SELinux and seccomp policy plus the GrapheneOS hardening, and in this case the mitigations succeeded (https://discuss.grapheneos.org/d/35110-grapheneos-is-protect...)
A LOT of websites are tenants on WHM/CPanel hosts. Not to mention how many agencies use it for their clients Wordpress sites.
They built it wrong.
I thought that was the entire design goal of the Unix model, didn't it originate in the times when hundreds of users logged on to a shared mainframe? There are still public Unix servers like SDF out there. SELinux is just an extra layer so that if someone gets root (ex. due to an exploit in your setuid code or cron jobs etc) it's not game over.
SDF used NetBSD. In the 90's they switched for a while for RH under X86. Worst era ever, very insecure. Now they use NetBSD X86-64.
On Hyperbola GNU/Linux, they will shift into OpenBSD, they got fed up with the corporate slopware (and propietary Linux became). They will still make Hyperbola BSD GNU-license compatible, from core to the userland tools.
In my case, I wish Emacs and GNU developers embraced plotutils and left out Gnuplot (is not GNU at all; worse, it conflicts with the GPL) and made Texinfo independent of LaTeX to produce PDF and HTML files with equations. Groff + troff+pic+eqn already do that, no Texlive needed. So can mandoc under OpenBSD, no magic needed, everything under few MB's.
Texlive it's huge (full instal it's over 7GB) and the so-called free FSDG is not 100% free, at all. With just that GNU Emacs would be truely GNU-standalone, relying on GNU tools for plots under Emacs' Calc and Texinfo books exported into PDF. A good plus for security.
Once you get that working, the rest would just follow their way. Also, GNU Hurd being developed with propietary LLM's/SAAS it's a disgrace against what GNU stands for too. They can go back to the right path, but they need will, for sure.
I'm quite sure there are many application hosting providers which rely on container runtime such as runC (default runtime of containerd/Docker), and a shared kernel between users.
In a just world, those companies would be held legally accountable for negligent practices. The Linux kernel upstream has made it clear for decades that security is a dirty word.
LPEs on Linux are obscenely commonplace.