Discovered three new serious “L1TF” vulnerabilities in Intel processors

Aug

15

2018

Intel has announced that three new serious vulnerabilities have been discovered in its processors, allowing unauthorized access to data in the L1 cache. The vulnerabilities are named L1 Terminal Fault, or L1TF.

Intel announces the existence of the L1TF vulnerabilities in an announcement and has put a page online with information about the measures that have been taken . Tech published all technical details about the new side channel attacks in a white paper about L1TF . The vulnerabilities are both in consumer processors and in Xeon server processors.

The first two variants relate to the Intel Software Guard Extensions and the System Management Mode. According to Intel, both can be solved with microcode and software updates and have already been released. The changes to the microcode have been made earlier this year and the updates for operating systems have been released on Tuesday.

CVE Name Ernst Score
CVE-2018-3615 L1 Terminal Fault-SGX High 7.9
CVE-2018-3620 L1 Terminal Fault-OS / SMM High 7.1
CVE-2018-3646 L1 Terminal Fault-VMM High 7.1
The third L1TF variant relates to virtual machines and although mitigations have also been released for this, Intel states that ‘further measures’ are needed depending on the situation. This applies to environments where it can not be guaranteed that all virtual machines are equipped with control systems with patched kernels. A possible measure is to use Core Scheduler in Windows Server 2016, or to disable HyperTreading altogether.

Intel claims that the security measures taken have little impact on performance and shows benchmarks of different scenarios before and after the implementation of the patches. Red Hat has also presented figures and shows that disabling HyperTreading can have a major negative impact on performance. This measure is not on consumer PCs.

Intel shows influence of L1TF patches on performanceIntel shows influence of L1TF patches on performanceIntel shows influence of L1TF patches on performanceIntel shows influence of L1TF patches on performance
The first vulnerability, CVE-2018-3615, was discovered by researchers at universities, including KU Leuven. They present the attack under the name Foreshadow and have set up a website with a paper and demonstration videos. The KU Leuven researchers shared their findings with Intel on 3 January 2018. Intel security researchers then found the other two related vulnerabilities themselves.

The publication of the new vulnerabilities has been coordinated by the security researchers, Intel and software companies. On Tuesday evening, various parties have put their analyzes online. Microsoft describes L1TF on its Technet blog and Oracle has put information online about which of its products have been affected. Red Hat also describes the vulnerabilities. According to Intel, there are no known cases of misuse of the leaks.

Video from Intel with simple explanation about L1 Terminal Fault

More detailed L1TF explanation by Red Hat

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