# CVE-2026-89920: KVM: s390: Fix memory corruption by not reinjecting CK machine checks

CVE-2026-89920 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-89920, released September 23, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-89920
- Priority: High
- CVSS: 7.8 (Important)
- EPSS: 0.0018
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 16, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-89920

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-89920](https://patchblox.com/security/data/fix/linux/debian-cve-2026-89920.md) | Sep 23, 2026 |
| Linux | linux Debian 14 | 7.2.6-1 | [DEBIAN-CVE-2026-89920](https://patchblox.com/security/data/fix/linux/debian-cve-2026-89920.md) | Sep 23, 2026 |

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Data as of 2026-11-08T06:59:42Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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