Tag Archives: Foreshadow

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.

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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.”

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

Thank you.

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Foreshadow Vulnerability Official Website:
https://foreshadowattack.eu/

Intel’s Blog Post:
https://newsroom.intel.com/editorials/protecting-our-customers-through-lifecycle-security-threats/

Intel’s FAQ Page:
https://www.intel.com/content/www/us/en/architecture-and-technology/l1tf.html

Intel’s Security Advisory:
https://www.intel.com/content/www/us/en/security-center/advisory/intel-sa-00161.html

Intel’s Software Developer Guidance:
https://software.intel.com/security-software-guidance/software-guidance/l1-terminal-fault

Red Hat’s Security Advisory:
https://access.redhat.com/security/vulnerabilities/L1TF

Linux Kernel Patch:
https://lore.kernel.org/patchwork/patch/974303/

Oracle’s Security Advisory:
https://blogs.oracle.com/oraclesecurity/intel-l1tf

Amazon Web Services’ Security Advisory:
https://aws.amazon.com/security/security-bulletins/AWS-2018-019/

Google Cloud Security’s Blog Post:
https://cloud.google.com/blog/products/gcp/protecting-against-the-new-l1tf-speculative-vulnerabilities

Microsoft Windows Azure’s Guidance:
https://docs.microsoft.com/en-us/azure/virtual-machines/windows/mitigate-se

Microsoft’s Windows Security Advisory (high level details):
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/ADV180018

Microsoft’s Technical Analysis of the Foreshadow Vulnerabilities:
https://blogs.technet.microsoft.com/srd/2018/08/10/analysis-and-mitigation-of-l1-terminal-fault-l1tf/

VMware Security Advisories:
https://www.vmware.com/security/advisories/VMSA-2018-0020.html

https://www.vmware.com/security/advisories/VMSA-2018-0021.html
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Videos:
Foreshadow Video (explains the first vulnerability very well):
https://www.youtube.com/watch?v=ynB1inl4G3c

Intel’s Video (explains all 3 vulnerabilities):
https://www.youtube.com/watch?v=n_pa2AisRUs

Demonstration of the Foreshadow attack:
https://www.youtube.com/watch?v=8ZF6kX6z7pM

Red Hat’s Video (explains all 3 vulnerabilities):
https://www.youtube.com/watch?v=kBOsVt0iXE4

Red Hat’s In-depth video of the 3 vulnerabilities:
https://www.youtube.com/watch?v=kqg8_KH2OIQ

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August 2018 Update Summary

Today Microsoft released updates to resolve 63 vulnerabilities (more formally known as CVEs (defined)).

This month also brings a new set of vulnerabilities affecting only Intel CPUs. I detail these more thoroughly in a separate post. However high level details are provided below.

Compared to previous months updates these have a smaller list of known issues (most of which have workarounds). Links to the relevant knowledge base (KB) articles are provided below:

KB4340731

KB4340733

KB4343885

KB4343892

KB4343897

KB4343900

KB4343909

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Adobe also released update for the following products:

Adobe Acrobat and Reader DC (priority 2, 2x CVEs)

Adobe Creative Cloud Desktop (priority 3, 1x CVE)

Adobe Experience Manager (priority 2, 3x CVEs)

Adobe Flash (priority 2, 5x CVEs)

As always if you use any of the above Adobe software, please update it as soon as possible especially in the case of Flash and Acrobat DC/Reader DC. Updates for Google Chrome will be available shortly either via a browser update or their component updater.

Please also review the out of band updates for Photoshop CC and Creative Cloud Desktop and apply them if you use these products.

You can monitor the availability of security updates for most your software from the following websites (among others) or use one of the utilities presented on this page:
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US Computer Emergency Readiness Team (CERT) (please see the “Information on Security Updates” heading of the “Protecting Your PC” page):

https://www.us-cert.gov/

A further useful source of update related information is the Calendar of Updates. News/announcements of updates in the categories of General SoftwareSecurity Software and Utilities are available on their website. The news/announcements are very timely and (almost always) contain useful direct download links as well as the changes/improvements made by those updates (where possible).

If you like and use it, please also consider supporting that entirely volunteer run website by donating.

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For this month’s Microsoft updates, I will prioritize the order of installation below:

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Microsoft Edge and Internet Explorer (multiple versions of Edge and IE affected)

Windows Font Library

Malicious LNK File

Microsoft Exchange

Foreshadow (L1TF) Vulnerabilities: Allow information disclosure via speculative execution; are only locally executable (rather than remotely). This vulnerability may allow one virtual machine to improperly access information from another. More details in my dedicated blog post.

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Please install the remaining updates at your earliest convenience.

As usual; I would recommend backing up the data on any device for which you are installing updates to prevent data loss in the rare event that any update causes unexpected issues. I have provided further details of updates available for other commonly used applications below.

Please find below summaries of other notable updates released this month.

Thank you.

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Nvidia Geforce Experience Software:
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In late August, Nvidia released a security advisory for their Geforce Experience software for Windows. This update resolves 3 high severity vulnerabilities (as per their CVSS base scores). The necessary updates can be obtained from here.

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VideoLAN VLC:
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On the final day of August, VideoLAN made available VLC 3.0.4. This appears to be a security update for Apple macOS due to the following entries within the releases notes (however it is unclear if this overflow is exploitable by an attacker):

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Text renderer:
* Fix head buffer overflow on macOS with some fonts
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For Linux and Windows this version provides fixes numerous non-security issues. Please update to version 3.0.4 to benefit from these improvements.

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Wireshark 2.4.9 and 2.6.3
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v2.4.9: 3 security advisories

v2.6.3: 3 security advisories

As per standard process Linux distributions can obtain this update using the operating systems standard package manager (if the latest version is not installed automatically using the package manager you can instead compile the source code (v2.6.3) or v2.4.9). This forum thread and this forum thread may also be helpful to you with installing Wireshark on your Linux based system.

For Mac OS X and Windows, the update is available within the downloads section of the Wireshark website. In addition, a detailed FAQ for Wireshark is available here.

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WinSCP:
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In late August; WinSCP version 5.13.1 was released upgrading it’s embedded OpenSSL version to 1.0.2p (which addresses 2x low severity CVEs (Link1 and Link2).

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OpenSSL
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On the 12 June and 16th April 2018; the OpenSSL Foundation issued 2 updates for OpenSSL to address 2x low severity security vulnerabilities as detailed in these security advisories (Link1 and Link2). To resolve these issues please update your OpenSSL installations to 1.1.0i (released 14th August) or 1.0.2o (released 14th August) (as appropriate).

FTP mirrors to obtain the necessary downloads are available from here.

Downloadable Tarballs (compressed/packaged code made for distribution) are available from here.

It should also be possible to use the package manager of a Linux/Unix operating system to update your OpenSSL installation as mentioned within the section titled “Installing updates for Linux distributions” on the “Protecting Your PC” page of this blog.

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VMware
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VMWare issued two security advisories for the following products during August:

Security advisory 1 (addresses 1 vulnerability of Important severity):

  • VMware Horizon 6
  • VMware Horizon 7
  • VMware Horizon Client for Windows
  • VMware Horizon View Agent
  • VMware Horizon Agents Installer (HAI)

Security advisory 2 (addresses 1 vulnerability of Critical severity):

  • VMware Workstation Pro / Player (Workstation)
  • VMware Fusion Pro, Fusion (Fusion)

If you use the above VMware products, please review the security advisories and apply the necessary updates.