x86: XPTI may break on huge-memory systems

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-79609
StatePUBLISHED
AssignerXEN
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-13 16:17:23 UTC
Updated2026-10-20 18:17:22 UTC
DescriptionXPTI (Xen Page Table Isolation) was introduced to mitigate Meltdown (CVE-2017-5754, one aspect of XSA-254). This involves copying 64-bit PV guest page table entries from guest-chosen root page tables to the Xen- chosen one which is in actual use by hardware. To read the guest root page table, the directmap is used. PV guests, however, have a directmap which may not cover all memory; in particular this is the case if any memory extends beyond the 5 TiB (CONFIG_BIGMEM=y: 3.5 TiB) address boundary.

Risk And Classification

Primary CVSS: v3.1 8.8 HIGH from ADP

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

EPSS: 0.001590000 probability, percentile 0.046070000 (date 2026-10-20)

Problem Types: CWE-284 | CWE-284 CWE-284 Improper Access Control

VersionSourceTypeScoreSeverityVector
3.1ADPDECLARED8.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
3.1134c704f-9b21-4f2e-91b3-4a467353bcc0Secondary8.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Xen Xen unknown consult Xen advisory XSA-516 Not specified

References

ReferenceSourceLinkTags
xenbits.xen.org/xsa/advisory-516.html af854a3a-2127-422b-91ae-364da2661108 xenbits.xen.org
xenbits.xenproject.org/xsa/advisory-516.html [email protected] xenbits.xenproject.org
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: This issue was discovered by George Dunlap. (en)

Additional Advisory Data

Workarounds

CNA: Not running 64-bit PV guests will avoid the vulnerability. The "mem=" hypervisor command line option may be used to limit the amount of memory Xen is going to use. That would be "mem=5T" for the CONFIG_BIGMEM=n case and "mem=3584G" for the CONFIG_BIGMEM=y one.

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