Both Variant 4 and Variant 3a could be exploited by a local attacker for this reason they have been rated “medium severity”
According to Oracle’s security advisory, Variant 4 affects Oracle Linux versions 6 and 7, and Oracle VM 3.4,
“Systems with microprocessors utilizing speculative execution and speculative execution of memory reads before the addresses of all prior memory writes are known may allow unauthorized disclosure of information to an attacker with local user access via a side-channel analysis, aka Speculative Store Bypass (SSB), Variant 4.” reads the security advisory published by Oracle.
Oracle has released software updates for the Oracle Linux distribution and Oracle VM virtualization products, along with the microcode updates provided by Intel.
“Two new processor vulnerabilities were publicly disclosed on May 21, 2018. They are vulnerabilities CVE-2018-3640 ( “Spectre v3a” or “Rogue System Register Read”) and CVE-2018-3639 (“Spectre v4” or “Speculative Store Buffer Bypass”). Both vulnerabilities have received a CVSS Base Score of 4.3.
Successful exploitation of vulnerability CVE-2018-3639 requires local access to the targeted system. Mitigating this vulnerability on affected systems will require both software and microcode updates.” states Oracle in a blog post
“Oracle will continue to release new microcode updates and firmware patches as production microcode becomes available from Intel,”
(Security Affairs – Oracle, Spectre and Meltdown attacks)