CVE-2021-4145 : What You Need to Know

A NULL pointer dereference issue was found in the block mirror layer of QEMU in versions prior to 6.2.0, allowing a malicious unprivileged guest user to crash the QEMU process on the host.

Understanding CVE-2021-4145

This CVE details a vulnerability in QEMU that could be exploited by an unprivileged user to cause a denial of service (DoS) attack on the host system.

What is CVE-2021-4145?

CVE-2021-4145 is a NULL pointer dereference vulnerability in QEMU versions before 6.2.0. It specifically occurs in the block mirror layer, where the

self

pointer is dereferenced without proper validation.

The Impact of CVE-2021-4145

The vulnerability allows an unprivileged user within the guest to crash the QEMU process on the host when writing data reaches the mirroring node threshold. This could lead to a DoS condition on the host system.

Technical Details of CVE-2021-4145

This section covers the specific technical aspects of the CVE.

Vulnerability Description

The vulnerability arises from the improper handling of the

self

pointer in the mirror_wait_on_conflicts() function, leading to a NULL pointer dereference issue.

Affected Systems and Versions

QEMU versions prior to 6.2.0 are affected by this vulnerability, specifically impacting systems using qemu-kvm 6.2.0.

Exploitation Mechanism

A malicious unprivileged user within the guest environment can exploit this vulnerability to crash the QEMU process on the host by triggering the mirroring node threshold.

Mitigation and Prevention

To mitigate the risks associated with CVE-2021-4145, immediate steps and long-term security practices should be followed.

Immediate Steps to Take

Apply the latest patches and updates provided by QEMU to address this vulnerability.
Monitor for any suspicious activities on the system that could indicate an exploitation attempt.

Long-Term Security Practices

Implement the principle of least privilege to limit the impact of potential vulnerabilities from unprivileged users.
Conduct regular security audits and assessments to identify and address any security gaps.

Patching and Updates

Ensure that your QEMU software is regularly updated to the latest version that includes fixes for CVE-2021-4145 to prevent any exploitation attempts.