CVE-2020-15565 : What You Need to Know

An issue was discovered in Xen through 4.13.x, allowing x86 Intel HVM guest OS users to cause a host OS denial of service or possibly gain privileges due to insufficient cache write-back under VT-d.

Understanding CVE-2020-15565

This CVE identifies a vulnerability in Xen that affects x86 Intel HVM guest OS users, potentially leading to denial of service or privilege escalation.

What is CVE-2020-15565?

The vulnerability in Xen through version 4.13.x allows malicious x86 Intel HVM guest OS users to exploit insufficient cache write-back under VT-d, potentially causing denial of service or privilege escalation on the host OS.

The Impact of CVE-2020-15565

Host OS denial of service or privilege escalation due to insufficient cache write-back under VT-d
Possibility of retaining read/write DMA access to frames returned to Xen's free pool
Potential for host crashes and privilege escalation

Technical Details of CVE-2020-15565

This section provides technical details about the vulnerability.

Vulnerability Description

The issue arises from insufficient cache write-back under VT-d in Xen, allowing x86 Intel HVM guest OS users to exploit the system.

Affected Systems and Versions

Xen versions from at least 3.2 onwards are affected
Only x86 Intel systems are vulnerable; x86 AMD and Arm systems are not affected
Only x86 HVM guests using hardware-assisted paging (HAP) with specific configurations are at risk

Exploitation Mechanism

Changes to shared page tables between IOMMU and CPU require flushing of both TLBs
IOMMUs may be non-coherent, necessitating writing back CPU cache to memory after changes
Malicious guests can retain read/write DMA access to frames in Xen's free pool

Mitigation and Prevention

Protecting systems from CVE-2020-15565 involves taking immediate steps and implementing long-term security practices.

Immediate Steps to Take

Apply patches provided by Xen to address the vulnerability
Monitor system logs for any suspicious activities
Restrict access to vulnerable systems

Long-Term Security Practices

Regularly update Xen and other software components
Implement strong access controls and least privilege principles
Conduct regular security audits and penetration testing

Patching and Updates

Stay informed about security advisories from Xen and related vendors
Apply security updates promptly to mitigate known vulnerabilities