Known simply as “Speculative Store Bypass” (Variant 4), this is the latest CPU flaw found by Google and Microsoft, and Intel has just released a statement explaining what the variant is and how you can protect yourself. Variant 4 uses speculative execution to potentially expose certain kinds of data through a side channel, allowing an attacker to read older memory in a CPU’s stack or other memory locations.
As listed out in the US-CERT alert, this vulnerability could allow less privileged code (and hence an attacker) to read arbitrary privileged data and run older commands speculatively, resulting in cache allocations that could be used to extract data by standard side-channel methods.
Intel says they’ve already delivered microcode updates for Speculative Store Bypass in Beta to OEMs, and they expect them to be more broadly released into production BIOS and software updates over the coming weeks. This mitigation will be set to off by default, giving consumers the choice of whether to enable it.
Intel says the expect most industry software partners to ship with the default-off option as when the patch is enabled they’ve observed a performance impact of approximately two to eight percent based on overall scores for benchmarks like SYSmark 2014 SE and SPEC integer rate on client and server test systems.
Red Hat has released a video about the exploit that you can view below.
As always, the advice to apply the latest patches once you get them, though it may be prudent to use a test environment to apply verify the patches before applying them wholesale.
Sources: The Verge, Intel, US-CERT, Red Hat, Microsoft, Google Project Zero
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