New Linux kernel security updates have been released for Ubuntu 17.10 (Artful Aardvark), Ubuntu 16.04 LTS (Xenial Xerus), Ubuntu 14.04 LTS (Trusty Tahr), and Ubuntu 12.04 ESM (Extended Security Maintenance), adding the compiler-based retpoline kernel mitigation for the Spectre Variant 2 vulnerability on amd64 and i386 architectures. Canonical fixed the Spectre Variant 2 security vulnerability last month on January 22, but only for 64-bit Ubuntu installations.
This update apparently mitigates the issue for 32-bit installations too. Spectre is a nasty hardware bug in microprocessors that use branch prediction and speculative execution and it could allow unauthorized memory reads via side-channel attacks.