This indicates an attack attempt to exploit an Information Disclosure vulnerability in various systems.
The vulnerability is due to how CPUs can be tricked to leak information from the kernel and other user-mode process memory. A remote attacker can exploit this to gain access to sensitive information. This signature covers for both Spectre and Meltdown vulnerability.
All systems that have CPUs with speculative execution and multiple levels of instruction/data cache.
Information Disclosure: Remote attackers can gain sensitive information from vulnerable systems.
See bottom of the following website for links to patches or updates from various vendors.