CVE-2021-3308 : Security Advisory and Response

This article provides detailed information about CVE-2021-3308, a vulnerability discovered in Xen versions 4.12.3 through 4.14.x that affects x86 HVM guests with PCI pass-through devices.

Understanding CVE-2021-3308

CVE-2021-3308 is a security flaw in Xen hypervisor that can lead to Denial of Service (DoS) attacks by exhausting the Interrupt Descriptor Table (IDT) vectors on the system.

What is CVE-2021-3308?

An x86 HVM guest with PCI pass-through capabilities can exhaust all IDT vectors on the system, disrupting proper functioning of PCI pass-through devices to other guests. This results in a DoS attack affecting the entire host.

The Impact of CVE-2021-3308

HVM guests with PCI pass-through devices can force allocation of all IDT vectors, causing a DoS attack that hampers the pass-through of PCI devices to other guests or the hardware domain.

Technical Details of CVE-2021-3308

This section outlines the technical aspects of the vulnerability.

Vulnerability Description

Xen versions 4.12.3 through 4.14.x allow x86 HVM guests with PCI pass-through capabilities to exhaust IDT vectors on the system, leading to a DoS attack.

Affected Systems and Versions

Xen versions 4.12.3 through 4.14.x are affected by this vulnerability, impacting systems with x86 HVM guests utilizing PCI pass-through devices.

Exploitation Mechanism

The vulnerability can be exploited by rebooting an x86 HVM guest with MSI or MSI-X capabilities enabled, which results in leaking vectors used by the MSI(-X) entries and exhaustion of IDT vectors.

Mitigation and Prevention

To protect systems from CVE-2021-3308, immediate steps can be taken along with long-term security practices.

Immediate Steps to Take

Update Xen to the latest patched version, apply vendor-supplied patches, and restrict access to vulnerable systems.

Long-Term Security Practices

Regularly update Xen hypervisor, monitor system logs for unusual activities, and implement access controls to prevent unauthorized exploitation.

Patching and Updates

Refer to security advisories from Xen Project, vendor-specific advisories, and apply patches promptly to mitigate the risk of exploitation.