Mitigating from CVE-2018-3646 on ESXi 6.7

To keep this short, new VCSA 6.7 has VUM built in. No more Flash needed. Yay finally.

So I upload the latest 6.7u3 image, create my baseline, and test remedy one of my simple laptop hosts. After system reboots and comes back on VCSA dashbaord… uhhh what’s with this yellow warning icon…. Summary…

OK great, so after years of Intel being ahead of AMD, looks like at the cost of some pretty shitty shortcuts. and these shortcuts have caused Intel a huge problem, and pretty everyone else. Since it affected everyone, everyone has some form of write up on it. In this case VMware has coded the above warning, with a reference to this KB, so you know read that if you want a dry overview.

As you can see I have what shows as 4 logical processors, but after applying the mitigation (setting VMkernel.Boot.hyperthreadingMitigation to true on the host advanced settings) and rebooting…

Yay the warnings gone, but apparently so are half my logical processors?

If your wondering why they didn’t enable this by default is due system resource management, which of course, is exactly what vSphere is. Since it affects the available resource of the host it may not be able to accommodate the workload it was originally designed for. In my case it’s a lab and my work load is obviously very light, and this isn’t an issue for me.

Was it worth the mitigation? I don’t really know at this point as I’m unaware of any easy simple tactics any attacker could use to attack my footprint. At the same type CPU resource is not my major constraint, it’s usually memory.

For now better safe than sorry. In my next post I hope to cover the vCenter upgrade path and an error that happened to me along the way, luckily it wasn’t that hard to recover from. 🙂

Cheers!

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