CVE-2026-89920 KVM: s390: Fix memory corruption by not reinjecting CK machine checks
A memory corruption vulnerability in the Linux kernel's KVM s390 subsystem allows attackers to potentially execute code or escalate privileges via improper machine check handling.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89920?
CVE-2026-89920 is a high-severity memory corruption vulnerability in Linux, published on 16 Sep 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:
KVM: s390: Fix memory corruption by not reinjecting CK machine checks
Channel-subsystem damage machine checks are for the host channel subsystem. The guest channel subsystem is emulated in the userspace VMM. There is no point in forwarding such machine checks into the guest.
This also simplifies the machine check reinjection and avoids kfree of a stack variable as reported by sashiko. There might be still machine checks that have the ck bit set with another bit (like instruction damage), mask out the CK bit in s390_backup_mcck_info(), like the CP and ED bits already are.
Which versions are affected by CVE-2026-89920?
How do I fix CVE-2026-89920?
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-2026-89920 being exploited?
There is no known exploitation of CVE-2026-89920 in the wild and no public exploit code.
Sources
Also known as AZL-101664, BELL-CVE-2026-89920, DEBIAN-CVE-2026-89920, GHSA-vhrh-h65f-3j9h, UBUNTU-CVE-2026-89920.