AMD and Google Disclose High-Severity Microcode Vulnerability in Zen CPUs
In a coordinated effort, AMD and Google have officially disclosed a high-severity microcode signature verification vulnerability affecting AMD’s Zen CPUs. The flaw, tracked as CVE-2024-56161, was inadvertently leaked last month when an Asus update page prematurely included a patch for the then-undisclosed issue.
The vulnerability, which carries a CVSS score of 7.2, allows an attacker with local administrator privileges to load malicious CPU microcode, possibly compromising the confidentiality and integrity of confidential workloads running under AMD’s Secure Encrypted Virtualization-Secure Nested Paging (SEV-SNP). As AMD stated in their advisory, “Improper signature verification in AMD CPU ROM microcode patch loader may allow an attacker with local administrator privilege to load malicious CPU microcode resulting in loss of confidentiality and integrity of a confidential guest running under AMD SEV-SNP.”
The issue was first brought to light on January 21, when Google vulnerability researcher Tavis Ormandy emailed the Open Source Security mailing list on SecLists.org, noting the Asus page’s premature disclosure. The page was later taken down, and AMD acknowledged the vulnerability but provided few details at the time.
The official disclosure on Monday was the result of a coordinated process between AMD and Google. AMD extended gratitude to Google researchers,including Ormandy,Josh Eads,Kristoffer Janke,Eduardo Vela,and Matteo Rizzo,for their role in identifying the flaw.
Mitigation measures are already available, requiring users to update the microcode for affected microprocessors.Some platforms may also need a firmware update for AMD’s SEV technology.Additional details on applying these mitigations can be found in AMD’s advisory.
In a separate advisory published on GitHub, Eduardo Vela provided further insights into the vulnerability. “This vulnerability allows an adversary with local administrator privileges (ring 0 from outside a VM) to load malicious microcode patches,” Vela wrote. “We have demonstrated the ability to craft arbitrary malicious microcode patches on Zen 1 through Zen 4 CPUs.”
The GitHub post also includes a proof-of-concept exploit and a timeline of events. google reported the issue on September 25, and a fix was implemented by December 17. Coordinated disclosure began on Monday, with Vela noting that the extended timeline was a “one-off exception to our standard vulnerability disclosure policy.”
“Due to the deep supply chain, sequence and coordination required to fix this issue, we will not be sharing full details at this time to give users time to re-establish trust on their confidential-compute workloads,” Vela added.”We will share additional details and tools on March 5, 2025.”
As of press time, neither AMD nor Google has responded to requests for additional information from Informa TechTarget.
| Key Details | Information |
|————————————-|———————————————————————————|
| Vulnerability | CVE-2024-56161 |
| CVSS Score | 7.2 |
| affected CPUs | AMD Zen 1 through Zen 4 |
| Mitigation | Microcode and firmware updates for SEV technology |
| Disclosure Timeline | Reported: September 25, 2024; Fixed: December 17, 2024; Disclosed: February 3, 2025 |
| full Details Release | March 5, 2025 |
This disclosure underscores the critical importance of securing CPU microcode and highlights the collaborative efforts between industry leaders to address vulnerabilities promptly. Users are urged to apply the necessary updates to safeguard their systems.
Q&A: Understanding the High-Severity Microcode Vulnerability in AMD Zen CPUs
Editor: Can you explain what this vulnerability (CVE-2024-56161) entails and why it’s considered high-severity?
Guest: certainly. This vulnerability lies in the microcode signature verification process of AMD’s Zen CPUs, spanning from Zen 1 to Zen 4. It carries a CVSS score of 7.2, which classifies it as high-severity. The flaw allows an attacker with local administrator privileges to load malicious microcode, potentially compromising the confidentiality and integrity of workloads running under AMD’s SEV-SNP technology. Essentially, it undermines the security of confidential computing environments.
editor: How was this vulnerability discovered, and what role did google play in its disclosure?
Guest: The issue was first noticed by Tavis Ormandy, a vulnerability researcher at google, who spotted it on an Asus update page that prematurely included a patch for the then-undisclosed flaw. Google’s team,including Ormandy,Josh Eads,Kristoffer Janke,Eduardo Vela,and Matteo Rizzo,worked closely with AMD to coordinate the disclosure process. Google reported the issue on September 25, 2024, and a fix was in place by December 17, 2024. The official disclosure occurred on february 3,2025,after a thorough collaboration between the two parties.
Editor: What are the potential risks if this vulnerability is exploited?
Guest: The primary risk is that an attacker with local admin privileges could load malicious microcode, disrupting the security of confidential workloads. This could lead to unauthorized access to sensitive data or even system-level compromises. Given that the flaw affects AMD’s SEV technology, which is designed to protect virtualized environments, the impact could be notably severe in cloud or enterprise settings where data confidentiality and integrity are paramount.
Editor: What mitigation measures are available, and how can users protect their systems?
Guest: AMD has released microcode updates to address the flaw. Additionally, some platforms may require a firmware update for SEV technology. Users are strongly encouraged to apply these updates immediately to mitigate the risk. AMD’s advisory provides detailed guidance on implementing these fixes.
Editor: Why is the full disclosure of the vulnerability delayed until March 5, 2025?
Guest: Due to the complexity of the supply chain and the extensive coordination required to address the issue, full details are being withheld to give users sufficient time to secure their systems. This delay ensures that organizations can rebuild trust in their confidential-compute workloads before more detailed facts is released. As Eduardo Vela noted, this is a one-off exception to Google’s standard vulnerability disclosure policy.
Editor: What broader implications does this vulnerability have for the industry?
Guest: This disclosure highlights the critical importance of securing CPU microcode, which is frequently enough overlooked but plays a fundamental role in system security. It also underscores the value of collaboration between industry leaders like AMD and Google in identifying and addressing vulnerabilities promptly.For organizations,this serves as a reminder to stay vigilant and apply security updates as soon as they become available.
Conclusion
The CVE-2024-56161 vulnerability in AMD Zen CPUs is a notable security issue that underscores the importance of microcode integrity and timely updates. With a CVSS score of 7.2, it poses a serious risk to confidential computing environments.Thanks to the collaborative efforts of AMD and Google,mitigation measures are now available,and users are urged to apply updates promptly. The delayed full disclosure until March 5, 2025, provides a window for organizations to secure their systems and rebuild trust in their workloads.