CVE-2026-72412 s390/mm: Fix handling of _PAGE_UNUSED pte bit
A flaw in the Linux kernel s390 memory management allows guest memory corruption and potential denial of service due to improper handling of the _PAGE_UNUSED bit.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-72412?
CVE-2026-72412 is a critical memory corruption vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-72412?
How do I fix CVE-2026-72412?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-72412 being exploited?
There is no known exploitation of CVE-2026-72412 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-72412, GHSA-94jh-p9fj-qxf8, UBUNTU-CVE-2026-72412.