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Vulnerabilities in AMD processors

Date :March 07, 2018

Publication: Article

During the month of March 2018, great media attention was given to the announcement by a previously little-known company for a series of 13 vulnerabilities affecting the latest version of AMD processors. After Spectre and Meltdown vulnerabilities, this type of hardware vulnerability attracts a lot of attention.

Overall these vulnerabilities are not considered critical, because they are not immediately usable for regular attacks.  However, they could be used by advanced attackers to carry out very sophisticated attacks. We therefore present here a summary of this event.

 

A highly criticized media campaign

The Israeli company CTS-Labs, which discovered these vulnerabilities, has been much criticized for the way it announced this discovery:

  • On one hand it publicly announced the existence of these vulnerabilities only one day after having transmitted all the technical details to AMD. This approach does not comply with the current "responsible disclosure" rules in which the discoverer gives the manufacturer time (for example 90 days) to prepare corrective measures. However, the CTS-Labs CTO explained the reason for this approach: by publicly announcing that vulnerabilities exist, without giving technical details, it can benefit from public opinion support to put pressure on the manifacturer and obtain fixes more quickly.
  • On the other hand the discoverer has prepared a very elaborate communication (dedicated website, explanation videos, names and logos for each type of attack, denigrating speech towards AMD) to announce these vulnerabilities and present them as catastrophic. So much so that some have argued (wrongly) that it could be a manipulation to make the price of AMD shares fall.

This excessive media campaign has been highly criticized by the security community and it has required the intervention of recognized experts to focus after a few days, on technical aspects of these vulnerabilities and the risks involved.

CTS-Labs had prepared several reports to describe the vulnerabilities:

  • A public report (available here and subsequently supplemented by this clarification) that gives only a vague description of vulnerabilities, insists on their severity and contains severe criticisms against AMD.
  • A secret report (still not publicly available), giving all the technical details, and which was communicated to AMD as well as to some recognized experts.

It was these experts who then publicly confirmed the reality of these vulnerabilities, and in particular Dan Guido from TrailOfBits.com who brought a lot of clarity on the technical reality of these problems in his blog.

 

But real vulnerabilities

The vulnerabilities concern systems designed around AMD's RYZEN (in different flavors) and EPYC processors. They do not exactly concern the central processor, but rather specialized coprocessors:

  • The Platform Security Processor (PSP, recently renamed "AMD Secure Processor"). It is a processor integrated in the same chip as the CPU, that provides security functions such as boot sequence validation or memory encryption for virtualized environments.
  • The "Promontery" chipset. It is a component present on the motherboard. It was developed by ASMedia Company.

 

There are 13 vulnerabilities grouped into 4 attack families:

  • MASTERKEY: These vulnerabilities (3) allow to bypass the signature verification mechanism when updating the PSP firmware. An attacker with admin rights can install that way any malicious firmware on the PSP.
  • FALLOUT and RYZENFALL: These are vulnerabilities (3+4) in the PSP firmware that allow memory changes leading to the execution of malicious code by the PSP processor or in the SMS mode (System Management Mode) of the central CPU.
  • CHIMERA: These vulnerabilities (2) concern the Promontery chipset. CT-Labs calls them "backdoors" because apparently the standard API allows to install arbitrary code on this chipset. The malicious code installed on the chipset by this way can access all the internal components of the computer (and in particular the RAM via DMA - Direct Memory Access).

Note: the 13th vulnerability is not associated with any of these 4 families. It is called "PSP Privilege Escalation" by CT-Labs and is not detailed. It is apparently less important than the others.

Globally these vulnerabilities are only accessible by an attacker who has already obtained full access to the target machine (i.e. already having "administrator" rights).

They allow him to:

  • Install malicious code inside internal hardware components (e.g. modifying the PSP firmware) and thus survive attempts to reinstall a clean system.
  • Execute code in very privileged contexts, out of the control of the operating system installed, and very difficult to detect.
  • Access to memory segments that allow to bypass protection mechanisms such as Windows 10's "Windows Credential Guard" (protection against attacks such as "Mimikatz").

So this is a complete corruption of computer's internal mechanisms and this is a very serious concern. However, according to Dan Guido, using these vulnerabilities to achieve a real attack still requires colossal work. It is likely that only very advanced (government type) attackers will be able to use these attacks.

These vulnerabilities (discovered in 6 months by a company with limited resources) clearly show that there are still many weaknesses in the internal architectures of computers. There will undoubtedly be many more such vulnerabilities discovered in the future. They are often referred to as "hardware vulnerabilities".

 

AMD patches coming soon?

AMD announced in its press release that it would release patches for these vulnerabilities in the coming weeks. According to CTS-Labs, this press release tries to minimize the severity of the found vulnerabilities and fixes are too difficult to develop to be provided in a few weeks.

 

Detailed timeline and resources

  • March 12, 2018: The Israeli company CTS-Labs sends AMD a "non-public" report detailing the 13 vulnerabilities discovered.
     
  • March 13, 2018: CTS-Labs makes the vulnerabilities public via a report (without technical details) and a dedicated website: AMDflaws.com. The security community strongly criticizes CTS-Labs' communication.
     
  • March 15, 2018: Dan Guido of the "Trail of bits" company announces that he had access to the details of the vulnerabilities as part of a "peer-review" service contracted by CTS-Labs and describes in an article the technical aspect of the vulnerabilities. It confirms that the vulnerabilities are serious but not as serious as the CTS-Labs communication might have thought. Alex Ionescu (a well-known security expert currently working at CrowdStrike.com) is also making similar statements on Twitter.
     
  • March 16, 2018: CTS-Labs publishes a complementary technical document called "Clarifications".
     
  • March 19, 2018: Check Point issues a short statement indicating that it also had details about some of the vulnerabilities and that they are true.
     
  • March 20, 2018: AMD releases a press statement (updated on March 21), confirming some of the vulnerabilities and announcing the release of patches in the coming weeks.
     
  •  March 21, 2018: CTS-Labs issues a response to AMD's press release.