Canonical has been playing a cat and mouse game with patches and vulnerabilities. Canonical has released an update that fixes boot failures of machines running Ubuntu 18.04 LTS and 16.04 LTS.
Earlier this month Canonica released security updates (USN-3695-1) for Ubuntu 18.04 LTS to fix six known vulnerabilities. According to the Ubuntu advisory, “Unfortunately, the fix for CVE-2018-1108 introduced a regression where insufficient early entropy prevented services from starting, leading in some situations to a failure to boot.”
The latest update fixes the regressions. Canonical urges users  to update their systems immediately. If you have installed any third party kernel modules you will have to recompile and reinstall them. 
“Due to an unavoidable ABI change the kernel updates have been given a new version number, which requires you to recompile and reinstall all third party kernel modules you might have installed. Unless you manually uninstalled the standard kernel metapackages
(e.g. linux-generic, linux-generic-lts-RELEASE, linux-virtual, linux-powerpc), a standard system upgrade will automatically perform this as well.”
This is the third time Canonical has released fixes in the last 30 days. In June, Canonical released a patch for Ubuntu 14.04 LTS that lead to boot failure on some machines.
Source: https://lists.ubuntu.com/archives/ubuntu-security-announce/2018-July/004503.html[1]

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