CVE-2020-25598 : Security Advisory and Response

An issue was discovered in Xen 4.14.x where a missing unlock in the XENMEM_acquire_resource error path can lead to a Denial of Service (DoS) attack. This vulnerability affects Xen 4.14 and later versions.

Understanding CVE-2020-25598

This CVE identifies a critical vulnerability in Xen hypervisor versions 4.14 and later that can be exploited to cause a host Denial of Service (DoS) attack.

What is CVE-2020-25598?

The vulnerability stems from a missing unlock in the error path of XENMEM_acquire_resource, potentially allowing a buggy or malicious HVM stubdomain to leak an RCU reference. This can result in subsequent administration operations, such as CPU offline, leading to a host DoS.

The Impact of CVE-2020-25598

The vulnerability affects Xen versions 4.14 and later, making them susceptible to a host DoS attack. While Xen 4.12 and 4.13 may not experience severe side effects, patches have been provided as a precautionary measure.

Technical Details of CVE-2020-25598

This section delves into the technical aspects of the vulnerability.

Vulnerability Description

The issue arises from a missing unlock in the XENMEM_acquire_resource error path, potentially allowing a leaked RCU reference by a buggy or malicious HVM stubdomain.

Affected Systems and Versions

Xen versions 4.14 and later are vulnerable to this DoS attack.
Only x86 HVM VMs with a Qemu stubdomain are generally at risk, while x86 PV and PVH domains, as well as ARM VMs, are typically not affected.

Exploitation Mechanism

Exploitation is possible by VMs using HVM stubdomains, while VMs with PV stubdomains or emulators running in dom0 are not susceptible.

Mitigation and Prevention

Protecting systems from CVE-2020-25598 requires immediate actions and long-term security practices.

Immediate Steps to Take

Apply provided patches promptly to mitigate the vulnerability.
Monitor system logs for any suspicious activities that could indicate an ongoing attack.

Long-Term Security Practices

Regularly update and patch the Xen hypervisor to address known vulnerabilities.
Implement strict access controls and network segmentation to limit the impact of potential attacks.

Patching and Updates

Stay informed about security advisories and updates from Xen to ensure timely patching of vulnerabilities.