CVE-2021-28696 Explained : Impact and Mitigation
Learn about CVE-2021-28696, an IOMMU page mapping issue affecting Xen on x86 systems. Understand the impact, technical aspects, and mitigation strategies for this critical vulnerability.
This article provides details about CVE-2021-28696, an IOMMU page mapping issue on x86 affecting Xen. Discover the impact, technical details, and mitigation strategies related to this vulnerability.
Understanding CVE-2021-28696
CVE-2021-28696 is a security vulnerability related to IOMMU page mapping issues on x86, impacting Xen virtualization software.
What is CVE-2021-28696?
The vulnerability allows guests with access to physical devices via PCI passthrough to manipulate memory mappings, potentially leading to privilege escalation, denial of service, or information leaks.
The Impact of CVE-2021-28696
The impact varies based on system configurations but can result in serious consequences like privilege escalation, denial of service attacks, or leakage of sensitive information on affected systems.
Technical Details of CVE-2021-28696
The vulnerability arises from Xen's inability to prevent guests from tampering with memory mappings on systems with ACPI tables specifying untranslated memory regions, especially affecting AMD systems.
Vulnerability Description
Xen fails to block guests from modifying memory mappings on systems with ACPI-specified memory regions meant to remain untranslated, leading to potential security breaches.
Affected Systems and Versions
Xen versions 4.11.x, xen-unstable, 4.12.x, 4.14.x, 4.15.x, and 4.13.x across various platforms are vulnerable to this issue.
Exploitation Mechanism
Exploitation involves guests manipulating memory mappings, particularly on AMD systems where identity mappings persist even after device de-assignment, allowing unauthorized access to memory ranges.
Mitigation and Prevention
Proactive measures are crucial to mitigate CVE-2021-28696 and prevent security risks associated with the vulnerability.
Immediate Steps to Take
Ensure untrusted guests do not have access to physical devices, limiting exposure to the vulnerability. Verify and remove any identity-mapped memory regions specified in ACPI tables.
Long-Term Security Practices
Regularly update Xen installations and monitor security advisories for patches addressing CVE-2021-28696. Implement robust access controls and device management practices to enhance system security.
Patching and Updates
Stay informed about security updates from Xen project and apply patches promptly to protect systems from potential exploits.