CVE-2019-18421 Explained : Impact and Mitigation

A vulnerability has been discovered in Xen versions 4.12.x and earlier, allowing x86 PV guest OS users to exploit race conditions in pagetable promotion and demotion operations to gain host OS privileges.

Understanding CVE-2019-18421

What is CVE-2019-18421?

An issue in Xen versions 4.12.x and earlier allows x86 PV guest OS users to escalate privileges by exploiting race conditions in pagetable operations.

The Impact of CVE-2019-18421

The vulnerability enables malicious PV guest administrators to elevate their privileges to that of the host OS, affecting all x86 systems with untrusted PV guests.

Technical Details of CVE-2019-18421

Vulnerability Description

Xen exposes hardware pagetables to guests, leading to race conditions in pagetable promotion and demotion operations.
Recursive promotions can cause significant delays, making restartable operations complex and prone to race conditions.

Affected Systems and Versions

Xen versions 4.12.x and earlier are affected.
All x86 systems with untrusted PV guests are vulnerable.

Exploitation Mechanism

Guests can exploit race conditions in pagetable operations to gain write access to in-use pagetables.
By manipulating pagetables, a malicious PV guest can escalate privileges to the host OS.

Mitigation and Prevention

Immediate Steps to Take

Apply security updates provided by Xen to patch the vulnerability.
Monitor Xen security advisories for any further updates.

Long-Term Security Practices

Regularly update Xen and other software to mitigate potential vulnerabilities.
Implement strict access controls and monitoring for guest OS activities.

Patching and Updates

Install the latest Xen security updates to address CVE-2019-18421.