Tag Archives: SGX

Vendors Respond to Foreshadow (L1TF) Vulnerabilities

Yesterday, academic and security researchers publically disclosed (defined) 3 new vulnerabilities affecting Intel CPUs (AMD and ARM are not affected).

What are these new vulnerabilities and what can they allow an attacker to do?
The first vulnerability known as Foreshadow or CVE-2018-3615 is used to extract data from an Intel SGX (Software Guard Extensions)(defined) secure enclave (area) by creating a shadow copy of the SGX protected data but that copy does not have the protection of SGX and can be read/accessed by the attacker. The attacker can also re-direct speculative execution into copying further private/sensitive into the shadow copied area while at the same time making it appear that area is genuine and thus has the same protection as the real SGX protected data.

The second vulnerability (part of a wider Foreshadow Next Generation (NG) group of two variants) known as CVE-2018-3620 allows the reading of data copied into the level 1 cache (defined) of a CPU (defined) when that data is in use by a computer operating system e.g. Red Hat Linux, Apple macOS or Microsoft Windows.

The third vulnerability is the second and final variant of the Foreshadow NG group known as CVE-2018-3646.  This affects virtualised environments. If a CPU thread (defined) being directed by an attacker is able to read the level 1 cache of a CPU that is also shared by another thread by a victim user (within another virtualised environment but using the same physical CPU) while that request will be blocked; if the information the attacker is looking to steal is in the level 1 cache they may still get a glimpse of this information.

How can I protect myself from these new vulnerabilities?
For the first and second vulnerabilities; the microcode (defined)/firmware (defined) updates made available earlier this year coupled with the newly released updates for operating systems linked to below will mitigate these two issues.


For the third vulnerability; affecting virtualised (defined) environments there are operating system updates and microcode/firmware updates available that will occasionally clear the contents of the level 1 cache meaning that when the attacker attempts to read it they will not receive any benefit from doing so. Partially removing the usefulness of the cache will have a performance impact from a few percent up to 15 percent in the worst case scenario.

However to completely mitigate this third vulnerability a capability known as Core Scheduling needs to be leveraged. This ensures that only trusted/non attacker controlled virtual machines have access to the same thread (this capability is already available in some virtual machine (hypervisor)(defined) environments).

However in some environments if it cannot be guaranteed that all virtual machines are trustworthy the disabling of Intel Hyper Threading (this means that only 1 thread will work per CPU core)(otherwise known as simultaneous multi-threading (SMT)(defined)) may be necessary and will more significantly impact performance than just the level 1 cache clearing.

In summary for this third vulnerability; depending upon the virtualised environment you are using and the trustworthiness of the virtual machines you are using will determine how many of the these extra security measure you will need to take.

To be clear I am NOT advocating that Intel Hyper Threading/SMT be disabled EN MASSE for security reasons. As per the advice in the linked to advisories (below)(specifically Intel and VMware) ; you MAY wish to disable Intel Hyper Threading/SMT to mitigate the third vulnerability (CVE-2018-3646) depending upon the environment your virtualised machines are operating.

This Ars Technica article explains it very well: “if two virtual machines share a physical core, then the virtual machine using one logical core can potentially spy on the virtual machine using the other logical core. One option here is to disable hyperthreading on virtual-machine hosts. The other alternative is to ensure that virtual machines are bound to physical cores such that they don’t share.”


Please find below links to vendor responses on these vulnerabilities as well as videos that can help in understanding these vulnerabilities:

Thank you.


Foreshadow Vulnerability Official Website:

Intel’s Blog Post:

Intel’s FAQ Page:

Intel’s Security Advisory:

Intel’s Software Developer Guidance:

Red Hat’s Security Advisory:

Linux Kernel Patch:

Oracle’s Security Advisory:

Amazon Web Services’ Security Advisory:

Google Cloud Security’s Blog Post:

Microsoft Windows Azure’s Guidance:

Microsoft’s Windows Security Advisory (high level details):

Microsoft’s Technical Analysis of the Foreshadow Vulnerabilities:

VMware Security Advisories:


Foreshadow Video (explains the first vulnerability very well):

Intel’s Video (explains all 3 vulnerabilities):

Demonstration of the Foreshadow attack:

Red Hat’s Video (explains all 3 vulnerabilities):

Red Hat’s In-depth video of the 3 vulnerabilities:


Details of Spectre Next Generation (NG) Vulnerabilities Emerging

Update: 23rd May 2018:
Please refer to the new blog post I have added to document and provide information on these new vulnerabilities.

Thank you.

Original Post:
Separate to my previous in-depth discussion of the Meltdown and Spectre vulnerabilities; I located this news article announcing the discovery of new vulnerabilities affecting Intel CPUs (and possibly ARM CPUs too). Few details are available; apart from that the vulnerabilities also affect Intel’s SGX (Software Guard Extensions)(defined) instructions and can be exploited within a virtual machine (defined) to gain access to the host (physical system).

It is likely further microcode updates from Microsoft and firmware update from Intel will be made available in the coming weeks. It is unknown if these new vulnerabilities dubbed Spectre Next Generation (NG) will be as serious as the original Meltdown and Spectre (Variants 1 and 2) disclosed in January.

On a related note (and discussed in another post); Microsoft resolved a regression in their Windows 10 Meltdown patch that was found by Windows Internals and security researcher Alex Ionescu. The fix was already included in Windows 10 Version 1803 (the April Update) and was provided to Version 1709 this month.

Thank you.