As you can imagine, the kernel security update patches the Ubuntu 18.04 LTS (Bionic Beaver) operating system against the recently disclosed Speculative Store Buffer Bypass (SSBB) side-channel vulnerability, also known as Spectre Variant 4 or CVE-2018-3639, which could let a local attacker expose sensitive information in vulnerable systems. Canonical also notes the fact that to fully mitigate Spectre Variant 4, users must also update the processor microcode firmware. They’ve been working with Intel to offer future microcode updates that fully address Spectre Variant 4, but AMD users will need to contact their vendor for firmware updates.