Researchers defend the Ryzenfall disclosure, explain why exploits are dangerous

Just months after Meltdown and Spectre were disclosed to the public, security researchers have uncovered another set of critical processor vulnerabilities. This time Intel owners can breathe easy: These exploits are unique to AMD’s processors, including its latest Ryzen chips.

“The Ryzen chipset, a core system component that AMD outsourced to a Taiwanese chip manufacturer, ASMedia, is currently being shipped with exploitable manufacturer backdoors inside,” reads the whitepaper put out by CTS Labs, the company that discovered the vulnerabilities. “CTS has been researching the security of AMD’s latest Zen processors for the past six months, including EPYC, Ryzen, Ryzen Pro and Ryzen Mobile, and has made concerning discoveries.”

CTS Labs released a letter clarifying some of the technical details of the exploits, in response to some criticism that has been leveled at the security firm regarding the plausibility that these exploits could even be put to use by a malicious actor.

“The vulnerabilities described in our site are second-stage vulnerabilities. What this means is that the vulnerabilities are mostly relevant for enterprise networks, organizations and cloud providers,” CTS Labs said in a statement. “The vulnerabilities described in could give an attacker that has already gained initial foothold into one or more computers in the enterprise a significant advantage against IT and security teams.”

That’s the real danger here. These exploits are unlikely to be used against you personally, but they pose a significant danger to large systems that handle sensitive data which could make appealing targets for enterprising hackers.

Disclosure dust-up

The announcement itself has generated a fair amount of controversy, as security research firm CTS Labs reportedly did not give AMD the industry-standard 90-day notice before announcing the existence of these exploits to the public.

In response, AMD has released a general statement which digs at CTS Lab’s unorthodox means of disclosure. “This company was previously unknown to AMD,” the statement reads, “and we find it unusual for a security firm to publish its research to the press without providing a reasonable amount of time for the company to investigate and address its findings.”

CTS Labs released its own response to the controversy in the form of a letter penned by Chief Technical Officer Ilia Luk-Zilberman. The letter outlines how CTS Labs first discovered the vulnerabilities, as part of an investigation into chip manufacturer ASMedia’s products. The letter suggests AMD inadvertently allowed the exploits to take root in its products by contracting with ASMedia for the design of Ryzen chipset components.

The speed and ease with which CTS Labs discovered these vulnerabilities, Luk-Zilberman alleges, contributed to the company’s decision to go public with the exploits well ahead of the typical 90-day window offered to companies like AMD when a serious vulnerability is discovered.

“I honestly think it’s hard to believe we’re the only group in the world who has these vulnerabilities, considering who are the actors in the world today, and us being a small group of six researchers,” Luk-Zilberman’s letter continues.

The letter goes on to describe CTS Labs’ opposition to the “responsible disclosure” norms within the cybersecurity industry. For example, when Google’s Project Zero uncovered the Meltdown and Spectre vulnerabilities, Google offered AMD and Intel a 200-day head start to get working on a patch. CTS Labs claims this relationship is bad for customers.

“I think that the current structure of ‘Responsible Disclosure’ has a very serious problem,” Luk-Zilberman said. “The main problem in my eyes with this model is that during these 30/45/90 days, it’s up to the vendor if it wants to alert the customers that there is a problem. And as far as I’ve seen, it is extremely rare that the vendor will come out ahead of time notifying the customers.”

Ryzenfall, Fallout, Master Key, and Chimera

Before we get into what these vulnerabilities are and how they work, let’s be clear about one thing: There are no patches for these vulnerabilities as of this writing. If you’re compromised, there is not much you can do about it at the moment. If you’re running a Ryzen processor, you’ll just have to be very careful for the next few weeks while we wait for a patch.

Ryzenfall exploit chart

Chart illustrating which products are affected by which vulnerabilities, credit CTS Labs.

“Firmware vulnerabilities such as Masterkey, Ryzenfall, and Fallout take several months to fix. Hardware vulnerabilities such as Chimera cannot be fixed and require a workaround,” CTS Labs reports. “Producing a workaround may be difficult and cause undesired side-effects.”

These vulnerabilities fall into four categories, dubbed Ryzenfall, Fallout, Masterkey, and Chimera. All four lead directly into the secure portion of AMD processors, where sensitive data like passwords and encryption keys are stored, but they achieve their goals in different ways.

“Attackers could use Ryzenfall to bypass Windows Credential Guard, steal network credentials, and then potentially spread through even highly secure Windows corporate network,” CTS Lab reports. “Attackers could use Ryzenfall in conjunction with Masterkey to install persistent malware on the Secure Processor, exposing customers to the risk of covert and long-term industrial espionage.”

The real danger of these vulnerabilities is their pervasive nature. Once someone has wormed their way into the secure processor via Ryzenfall or Masterkey, they are there for good. They can set up camp and spread throughout the network virtually undetected. This is a scary prospect for individuals, but for AMD’s enterprise customers, like Microsoft, it could mean the exposure of very sensitive data to malicious actors on a large scale.

Updated on March 15: Added CTS Labs revised disclosure.