Critical Vulnerability in Xen Package: CVE-2021-28710 - Shared Page Table Mode Issue
Summary
ALPINE-CVE-2021-28710: certain VT-d IOMMUs may not work in shared page table mode For efficiency reasons, address translation control structures (page tables) may (and, on suitable hardware, by default will) be shared between CPUs, for second-... Affects xen versions < 4.15.1-r1. Fixed in 4.15.1-r1. How to fix ↓
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Background
Xen is a popular open-source hypervisor that allows multiple operating systems to run concurrently on a single physical machine. It provides virtualization capabilities, enabling efficient resource management and isolation between virtual machines. However, certain configurations of Xen may expose vulnerabilities, such as CVE-2021-28710, which affects its handling of VT-d IOMMUs in shared page table mode.
Vulnerability Detail
CVE-2021-28710 is a vulnerability in the Xen hypervisor that arises from improper handling of address translation control structures (page tables) when shared between CPUs. Specifically, the issue occurs in configurations where an IOMMU requires only three levels of page tables instead of the default four. The Xen hypervisor fails to strip the top-level table before inserting the root table's address into the hardware pagetable base register. This oversight allows a guest operating system to write to leaf page table entries, potentially leading to unauthorized access to memory and compromising the integrity of the hypervisor and other virtual machines.
How To Fix
Minimum fixed version
4.15.1-r1
This is the first release that contains the fix.
sudo apk add --upgrade xenTip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
As a temporary workaround, if updating the package is not immediately feasible, consider disabling shared page table mode in your Xen configuration. This may reduce the risk of exploitation until a proper update can be applied. However, this may impact performance and should be evaluated carefully.
Conclusion
CVE-2021-28710 represents a critical vulnerability in the Xen hypervisor that can lead to severe security risks if left unaddressed. Users are strongly encouraged to update to the patched version to ensure the security of their virtualized environments. Utilizing tools like Vulert can help monitor and alert for such vulnerabilities in real-time.
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FAQ
CVE-2021-28710 is a vulnerability in the Xen hypervisor that affects its handling of shared page tables, potentially allowing unauthorized memory access.
The CVSS score for CVE-2021-28710 is 8.8, indicating a critical level of severity that requires immediate attention.
You can use Vulert's playground at Vulert Scanner to check if your application is affected by this vulnerability without requiring any signup.
Exploitation of this vulnerability could lead to unauthorized access to memory, compromising the integrity of the hypervisor and other virtual machines running on the host.
Yes, a patch is available in version 4.15.1-r1 of the Xen package. It is recommended to update to this version or later to mitigate the vulnerability.
References
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