Foreshadow: the fifth major CPU security flaw discovered in 2018

ZMsiXone · Aug 14, 2018

Source: https://www.techspot.com/news/75971-foreshadow-fifth-major-cpu-security-flaw-discovered-2018.html

A hot potato: The dust has barely settled over the Spectre and Meltdown vulnerabilities and now security researchers are looking at a whole new hardware flaw that could be potentially worse. They are calling it Foreshadow and it is similar to Spectre, but affects one of the most secure elements of Intel chips -- Software Guard Extensions or SGX.
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Intel has rated Foreshadow as 'high severity' and confirmed that the flaw affects all SGX-enabled Core processors, while Intel Atom CPUs are unaffected. The list below comes straight from the CPU maker who has opened a security advisory page with additional technical details:

Intel Core i3/i5/i7/M processor (45nm and 32nm)

2nd/3rd/4th/5th/6th/7th/8th generation Intel Core processors

Intel Core X-series Processor Family for Intel X99 and X299 platforms

Intel Xeon processor 3400/3600/5500/5600/6500/7500 series

Intel Xeon Processor E3 v1/v2/v3/v4/v5/v6 Family

Intel Xeon Processor E5 v1/v2/v3/v4 Family

Intel Xeon Processor E7 v1/v2/v3/v4 Family

Intel Xeon Processor Scalable Family

Intel Xeon Processor D (1500, 2100)

As of writing, only Intel CPUs have been confirmed to be vulnerable to Foreshadow. In order to secure systems against the two Foreshadow variants, mitigations will be required at both the software level (OS, VM, VMM, etc.) and microcode level (hardware firmware, BIOS).
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ronjor · Aug 14, 2018

Protecting Our Customers through the Lifecycle of Security Threats

Details and Mitigation Information for L1 Terminal Fault
By Leslie Culbertson
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B-boy/StyLe/ · Aug 14, 2018

https://support.microsoft.com/en-us/help/4343898/windows-81-update-kb4343898

Provides protections against a new speculative execution side-channel vulnerability known as L1 Terminal Fault (L1TF) that affects Intel® Core® processors and Intel® Xeon® processors (CVE-2018-3620 and CVE-2018-3646). Make sure previous OS protections against Spectre Variant 2 and Meltdown vulnerabilities are enabled using the registry settings outlined in the Windows Client and Windows Server guidance KB articles. (These registry settings are enabled by default for Windows Client OS editions, but disabled by default for Windows Server OS Editions.)
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hawki · Aug 15, 2018

"Intel releases fix for latest chip security flaw..."

https://www.computerweekly.com/news/252446889/Intel-releases-fix-for-latest-chip-security-flaws

"...The first two variants were patched in a microcode released as part of INTEL-SA-00115 in May/June this year, though it wasn't mentioned at the time. The third variant, affecting Hypervisor software, as used in virtualisation, has only just to get patches delivered, with rollout starting yesterday..."

https://hexus.net/tech/news/cpu/121115-intel-releases-updates-foreshadow-cpu-flaws/

reasonablePrivacy · Aug 15, 2018

Theo on the latest Intel issues

These 3 issues all relate to a bug in Intel cpus
The cpu will speculatively honour invalid PTE against data in the
on-core L1 cache. Memory disclosure occurs into the wrong context.
These 3 issues (CVE-2018-3615, CVE-2018-3620, CVE-2018-3646) together
are the currently public artifacts of this one bug.
[..]
CVE-2018-3615 (Foreshadow) is by receiving the most press which is
amazing considering it is by far the most boring of the 3, since very
few few people give a rats ass about SGX -- who cares if SGX is broken
when the cpu can't run your OS safely? Some convincing press agencies
were hired I guess, and have performed a masterful job of distracting.
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ronjor · Aug 17, 2018

Industry Reactions to Foreshadow Flaws: Feedback Friday

By Eduard Kovacs on August 17, 2018
Industry professionals have commented on various aspects of Foreshadow/L1TF, including its impact on various types of systems, difficulty of exploitation, and performance issues introduced by mitigations.
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guest · Aug 7, 2020

Foreshadow returns to the foreground: Secrets-spilling speculative-execution Intel flaw lives on, say boffins
A misunderstanding about the vulnerability means defenses fall short
August 7, 2020
https://www.theregister.com/2020/08/07/foreshadow_strikes_back_boffins_find/

Some of the boffins who in 2018 disclosed the data-leaking speculative-execution flaws known as Spectre and Meltdown today contend that attempts to extinguish the Foreshadow variant have missed the mark.

The paper, Speculative Dereferencing of Registers: Reviving Foreshadow, details how defenses based on this misunderstanding, such as the Meltdown mitigation known as KAISER, don't really work against Foreshadow.
"The consequence is that we are able to mount a Foreshadow attack on older kernels patched against Foreshadow with all mitigations enabled and on a fully-patched kernel if only Spectre-v2 mitigations are disabled."

Thus, if you've used the nospectre_v2 kernel option on your fully-patched Intel-powered Linux server to optimize for speed over security, and think it won't affect your Foreshadow protection, think again: the machine is now vulnerable to Foreshadow.
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It also means Foreshadow can potentially affect CPU cores from vendors other than Intel, such as AMD, Arm, and IBM, and that the effects can be triggered by malicious JavaScript in a browser window, though fairly slowly based on the scenarios described in the paper.
The good news is that there is a defense against the Foreshadow L3 attack described in the paper: implementing the Spectre-BTB (Branch Target Buffer) countermeasures.
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Paper: Speculative Dereferencing of Registers:Reviving Foreshadow
(PDF - 874 KB): [PLAIN]https://arxiv.org/pdf/2008.02307[/PLAIN]

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