CVE-2021-28701 Explained : Impact and Mitigation
Discover the impact of CVE-2021-28701, a vulnerability in Xen allowing guests to maintain access to de-allocated memory pages, potentially leading to privilege escalation and data leaks. Learn about affected systems, exploitation risks, and prevention methods.
A race condition in XENMAPSPACE_grant_table handling allows guests to retain access to memory pages that were freed, potentially leading to privilege escalation, Denial of Service (DoS), or information leaks. This issue was discovered by Julien Grall of Amazon.
Understanding CVE-2021-28701
This vulnerability in Xen affects certain versions, enabling a malicious guest to exploit the hypervisor's missing enforcement, impacting both host and guest systems.
What is CVE-2021-28701?
Guests could maintain access to de-allocated memory pages in Xen, posing risks of elevated privileges, DoS, and data leakage during guest switches, impacting both host and guest systems.
The Impact of CVE-2021-28701
A malicious guest could potentially escalate privileges to the host's level, trigger DoS attacks, or compromise data integrity through information leaks.
Technical Details of CVE-2021-28701
This vulnerability affects Xen versions 4.0 onwards, while version 3.4 and older remain unaffected. Only x86 HVM and PVH guests leveraging grant table version 2 interfaces are vulnerable.
Vulnerability Description
Guests can retain access to freed memory pages due to missing enforcement, enabling unauthorized access during guest switches, potentially leading to security breaches.
Affected Systems and Versions
Xen versions 4.0 onwards are impacted, specifically x86 HVM and PVH guests using grant table version 2 interfaces. Older versions and x86 PV guests are not affected.
Exploitation Mechanism
A malicious guest can exploit the race condition in XENMAPSPACE_grant_table handling to maintain access to de-allocated memory pages, potentially causing privilege escalation, DoS, or data leaks.
Mitigation and Prevention
To address CVE-2021-28701, consider immediate actions and adopt long-term security practices.
Immediate Steps to Take
Running only PV guests or suppressing the use of grant table v2 interfaces for HVM or PVH guests can mitigate this vulnerability.
Long-Term Security Practices
Regularly update Xen to patched versions, implement security best practices, and conduct regular vulnerability assessments to enhance system security.
Patching and Updates
Refer to official vendor advisories, such as FEDORA-2021-11577e5229, FEDORA-2021-fed53cbc7d, DSA-4977, FEDORA-2021-5a0c7bc619, and GLSA-202208-23, for patching instructions and updates.