CVE-2023-4155 : What You Need to Know

A flaw was discovered in KVM AMD Secure Encrypted Virtualization (SEV) in the Linux kernel, specifically affecting systems with multiple virtual CPUs using SEV-ES or SEV-SNP. This vulnerability could lead to a double fetch race condition, potentially resulting in a denial of service attack or even a guest-to-host escape in kernel configurations without stack guard pages.

Understanding CVE-2023-4155

This section will delve into the details of CVE-2023-4155, including what the vulnerability entails and its potential impact.

What is CVE-2023-4155?

CVE-2023-4155 is a vulnerability found in KVM AMD Secure Encrypted Virtualization (SEV) in the Linux kernel. It allows a KVM guest to trigger a double fetch race condition vulnerability when using SEV-ES or SEV-SNP with multiple virtual CPUs, potentially leading to a stack overflow and subsequent denial of service or guest-to-host escape.

The Impact of CVE-2023-4155

The impact of this vulnerability lies in its ability to be exploited by an attacker to trigger a denial of service attack or execute a guest-to-host escape in certain kernel configurations where stack guard pages are not present (e.g.,

CONFIG_VMAP_STACK

).

Technical Details of CVE-2023-4155

In this section, we will explore the vulnerability description, affected systems and versions, as well as the exploitation mechanism of CVE-2023-4155.

Vulnerability Description

The vulnerability in CVE-2023-4155 arises from a double fetch race condition within KVM AMD Secure Encrypted Virtualization (SEV) in the Linux kernel. This can be triggered when a KVM guest utilizing SEV-ES or SEV-SNP with multiple virtual CPUs invokes the

VMGEXIT

handler recursively.

Affected Systems and Versions

The systems affected by CVE-2023-4155 include various versions of Red Hat Enterprise Linux (6, 7, 8, 9), Fedora, and the kernel itself. Specific package information and statuses can be found through the provided collection URLs.

Exploitation Mechanism

To exploit CVE-2023-4155, an attacker would need to trigger the double fetch race condition by invoking the

VMGEXIT

handler multiple times, potentially leading to a stack overflow. This could result in a denial of service attack or a guest-to-host escape in vulnerable kernel configurations.

Mitigation and Prevention

Mitigating the risks associated with CVE-2023-4155 involves taking immediate steps to secure affected systems, implementing long-term security practices, and ensuring timely patching and updates.

Immediate Steps to Take

Organizations should apply relevant security updates and patches provided by Red Hat or other affected vendors.
It is crucial to monitor for any signs of unauthorized access or anomalous activity on potentially impacted systems.
Consider limiting access to vulnerable systems and implementing additional security measures as needed.

Long-Term Security Practices

Regularly update and patch all software and systems to address known vulnerabilities promptly.
Conduct security assessments and penetration testing to identify and mitigate potential security weaknesses.
Educate personnel on best practices for cybersecurity, including recognizing and responding to potential threats.

Patching and Updates

Red Hat and other affected vendors may release patches or updates to address CVE-2023-4155. Organizations should prioritize the installation of these updates to protect their systems and data from exploitation.