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TI-2026-71803 Aliases CVE-2026-79609GHSA-842c-7fjj-j8jj

x86 XPTI in Xen may break on systems with huge memory

Priority LOW 39CWE-284Published · Updated

Key facts

Attack vector
Local
Privileges required
Low
User interaction
None
Attack complexity
Low
Impact type
Security bypass
Confidentiality · integrity · availability
High · High · High
Fix status
No fix listed

Attack profile from CVSS 3.1 · CISA ADP. Fix status from CNA. Impact type from CWE-284.

Summary

Xen's x86 XPTI (Xen Page Table Isolation), a mitigation for Meltdown, may break on systems with memory beyond the 5 TiB boundary (3.5 TiB with CONFIG_BIGMEM=y). PV guests have a directmap that may not cover all memory, so copying their page table entries can fail (CWE-284). A local user with low privileges can affect confidentiality, integrity and availability, with a scope change.

Written with Claude Haiku 5.5 from the sources below · 2026-10-27

Description from the CNA

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00106 1st percentileScored 2026-11-07
Fix No fix listed No fixed version in the sources yet

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Total

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
XenXen——No fix listedCNA
  • Xen VendorXen Affected — Fixed in — No fix listed CNA

Remediation

No fixed version of Xen is listed.

Written with Claude Haiku 5.5 from the sources below · 2026-10-27

Vendor assessments

Red Hat

Red Hat's page for this CVE →

Not affected: 1 product
  • Red Hat

Timeline

  1. 2026-10-13 Threatist record created from CVE-2026-79609
  2. 2026-10-13 Alias added: GHSA-842c-7fjj-j8jj
  3. 2026-10-20 CVSS score added · CISA ADP
  4. 2026-10-20 Weakness changed · CISA ADP
  5. 2026-10-20 CISA SSVC decision points changed
  6. 2026-10-23 Affected versions changed · Red Hat
  7. 2026-10-23 CVSS score added · Red Hat

References

Other 1

  • TI-2012-00210 The x86-64 kernel system-call functionality in Xen 4.1.2 and earlier, as used in Citrix… CVSS 2.0HIGH 7.2
  • TI-2023-07042 Information disclosure through error messages in AMD Ryzen™ 3000 Series Desktop… CVSS 3.1MEDIUM 5.5
  • TI-2015-04333 The C+ mode offload emulation in the RTL8139 network card device model in QEMU, as used… CVSS 2.0HIGH 9.3
  • TI-2015-06741 The KVM subsystem in the Linux kernel through 4.2.6, and Xen 4.3.x through 4.6.x, allows… CVSS 3.1CRITICAL 10.0
  • TI-2018-06436 A statement in the System Programming Guide of the Intel 64 and IA-32 Architectures… CVSS 3.0HIGH 7.8
  • TI-2024-20522 x86: Incorrect logic for BTC/SRSO mitigations CVSS 3.1HIGH 7.5
See all 541 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences