CVE-2026-79609
Published Oct 13, 2026
Modified Oct 13, 2026
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.
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References
Frequently Asked Questions
What is CVE-2026-79609? +
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.
How do I check if I'm vulnerable to CVE-2026-79609? +
You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.