CVE-2021-28700 : What You Need to Know

A memory limit issue in Xen's dom0less feature can lead to denial of service attacks. Learn about the impact, affected systems, and mitigation steps.

Understanding CVE-2021-28700

This CVE refers to a vulnerability in Xen that allows a malicious guest to drive Xen out of memory, potentially resulting in a Denial of Service (DoS) attack affecting the entire system.

What is CVE-2021-28700?

The vulnerability in Xen's dom0less feature allows unprivileged domains to allocate memory beyond the administrator's configured limit. It impacts Arm systems and versions of Xen since 4.12.

The Impact of CVE-2021-28700

A malicious dom0less guest could exhaust Xen's memory, leading to a DoS attack that affects the entire system. This can result in service disruption and system instability.

Technical Details of CVE-2021-28700

Here are the technical details regarding the vulnerability:

Vulnerability Description

The dom0less feature in Xen allows domains to allocate memory without a set limit, potentially driving Xen out of memory.

Affected Systems and Versions

Arm systems running Xen versions since 4.12 are vulnerable to this memory limit issue.

Exploitation Mechanism

By leveraging the dom0less feature, an attacker can create unprivileged domains that allocate memory beyond the administrator's configured limits, causing a DoS attack.

Mitigation and Prevention

To address CVE-2021-28700, consider the following mitigation strategies:

Immediate Steps to Take

There is no known workaround for this vulnerability. It is recommended to monitor system resources and apply security updates promptly.

Long-Term Security Practices

Maintain up-to-date security patches for Xen and regularly review system configurations to ensure memory allocation limits are properly set.

Patching and Updates

Refer to vendor advisories such as the ones provided by Fedora, Debian, and Gentoo for patching information and updates.