CVE-2021-3930 : What You Need to Know

An off-by-one error found in the SCSI device emulation in QEMU could allow a malicious guest to crash QEMU, resulting in a denial of service condition.

Understanding CVE-2021-3930

This section will cover the details of CVE-2021-3930, its impact, technical details, and mitigation steps.

What is CVE-2021-3930?

CVE-2021-3930 is an off-by-one error discovered in the SCSI device emulation in QEMU. The vulnerability may be triggered during the processing of MODE SELECT commands under specific conditions.

The Impact of CVE-2021-3930

The vulnerability could be exploited by a malicious guest to potentially crash QEMU, leading to a denial of service scenario. This can impact the availability and stability of the system.

Technical Details of CVE-2021-3930

Let's delve into the technical aspects of CVE-2021-3930 to better understand the vulnerability, affected systems, and the exploitation mechanism.

Vulnerability Description

The off-by-one error occurs in the SCSI device emulation component of QEMU when processing MODE SELECT commands. Specifically, if the 'page' argument is set to MODE_PAGE_ALLS (0x3f), the flaw can be triggered.

Affected Systems and Versions

The vulnerability affects QEMU with version qemu-kvm 6.2.0-rc0. Users of this version are advised to take immediate action to secure their systems.

Exploitation Mechanism

A malicious actor could exploit this vulnerability by sending specially crafted MODE SELECT commands to the vulnerable QEMU instance, causing it to crash and leading to a denial of service condition.

Mitigation and Prevention

To protect systems from the risks associated with CVE-2021-3930, it is crucial to implement the following immediate steps and establish long-term security practices.

Immediate Steps to Take

Update QEMU to a patched version that addresses the off-by-one error.
Monitor network traffic for any suspicious activity that could indicate an exploitation attempt.

Long-Term Security Practices

Regularly update software and apply security patches to mitigate known vulnerabilities.
Implement network segmentation and access controls to limit the impact of potential attacks.

Patching and Updates

Stay informed about security advisories and updates from QEMU and relevant vendors to ensure timely patching of vulnerabilities.