CVE-2026-72412
Received Received - Intake

Linux Kernel Page Table Handling Flaw

Publication date: 2026-08-15

Last updated on: 2026-08-15

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: s390/mm: Fix handling of _PAGE_UNUSED pte bit The _PAGE_UNUSED softbit should not really be lying around. Its sole purpose is to signal to try_to_unmap_one() and try_to_migrate_one() that the page can be discarded instead of being moved / swapped. KVM has no way to know why a page is being unmapped, so it sets the bit on userspace ptes corresponding to unused guest pages every time they get unmapped. KVM has no reasonable way to clear the bit once the page is in use again. While set_ptes() checks and clears the bit, other paths that set new ptes did not. This led to used pages being thrown out as if they were unused, causing guest corruption. Fix the issue by clearing the _PAGE_UNUSED bit for present ptes in set_pte(), i.e. whenever a present pte is getting set. The check in set_ptes() is then redundant and can be removed. Also fix gmap_helper_try_set_pte_unused() to only set the bit if the pte is present; the _PAGE_UNUSED bit is only defined for present ptes and thus should not be set for non-present ptes.

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Meta Information

Published
2026-08-15
Last Modified
2026-08-15
Generated
2026-08-15
AI Q&A
2026-08-15
EPSS Evaluated
N/A
NVD
CVE-2026-72412
EUVD
EUVD-2026-59311

Affected Vendors & Products

Currently, no data is known.

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Exploitability

CWE
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KEV
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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability in the Linux kernel involves incorrect handling of the _PAGE_UNUSED page table entry (PTE) bit. The bit is meant to indicate unused pages that can be discarded, but KVM sets it on userspace PTEs for unmapped guest pages without a way to clear it when pages are reused. This causes used pages to be treated as unused and discarded, leading to guest memory corruption.

Detection Guidance

This vulnerability is specific to the Linux kernel's memory management on s390 architecture. Detection requires checking kernel logs for memory corruption events or guest corruption issues related to page unmapping. No standard commands are provided in the context.

Impact Analysis

If you use virtualization with KVM on s390x systems, this flaw could corrupt guest memory, leading to crashes, data loss, or security issues in virtual machines. Systems not using KVM or s390x architecture are unaffected.

Mitigation Strategies

Apply the kernel patch that fixes the _PAGE_UNUSED bit handling in set_pte() and gmap_helper_try_set_pte_unused(). Update to a patched kernel version where this issue is resolved.

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