CVE-2021-28694

CVE-2021-28694: vulnerability in xen

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3Vexday Risk Score

No sign of exploitation. No public exploitation artifact known so far.

ssvc Trackepss 0.4%
In short

Xen hypervisor fails to properly restrict memory access on systems with IOMMU (input/output memory management unit). Guests can bypass security restrictions and access memory regions they shouldn't, potentially compromising the entire system.

Technical detail

On x86 systems, Xen does not adequately enforce ACPI-specified untranslated memory regions in IOMMU page mappings, allowing guest VMs to modify or replace these mappings. AMD systems exhibit additional flaws: discontinuous exclusion ranges are incompletely mapped, and device de-assignment leaves identity mappings intact, granting persistent unauthorized memory access to previously-assigned devices.

Summary generated and translated by AI from the official description.
IOMMU page mapping issues on x86 T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Both AMD and Intel allow ACPI tables to specify regions of memory which should be left untranslated, which typically means these addresses should pass the translation phase unaltered. While these are typically device specific ACPI properties, they can also be specified to apply to a range of devices, or even all devices. On all systems with such regions Xen failed to prevent guests from undoing/replacing such mappings (CVE-2021-28694). On AMD systems, where a discontinuous range is specified by firmware, the supposedly-excluded middle range will also be identity-mapped (CVE-2021-28695). Further, on AMD systems, upon de-assigment of a physical device from a guest, the identity mappings would be left in place, allowing a guest continued access to ranges of memory which it shouldn't have access to anymore (CVE-2021-28696).
Affected products
Xen · xen
Related CVEs — xen

In the same product, most dangerous first.

CVE-2021-28706—CVE-2021-28706EPSS 2.2%CVE-2021-28700—CVE-2021-28700EPSS 1.9%CVE-2022-42330—CVE-2022-42330EPSS 1.4%CVE-2022-42333—CVE-2022-42333EPSS 1.2%CVE-2021-28690—CVE-2021-28690EPSS 1.0%CVE-2022-26364—CVE-2022-26364EPSS 0.5%