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CVE-2026-79609x86: XPTI may break on huge-memory systems

Description

XPTI (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.

Timeline

  1. ID reserved

    By XEN

  2. · 49 days later

    Published

  3. · 7 days later

    Record updated

Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.

Scores

CVSS scores of CVE-2026-79609, by who scored it
Scored byCVSSScoreVector
CISA-ADPADP (enrichment)3.1High8.8CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
NVDNVD · Awaiting Analysis3.1High8.8CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
EPSS (exploitation in 30 days)
0.11% · top 99% of all CVEs (14 Nov 2026)
CISA SSVC
Exploitation: none · Automatable: no · Technical impact: total
Loading the EPSS history…

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 8.8.

Affected products

  • Xen · Xen

    • unknown consult Xen advisory XSA-516

What to do

Workaround: 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.

References

References2

Sources

The same CVE in the primary databases and aggregators, to check against.

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Record last updated .