CVE-2026-89957: Linux Vulnerability (CVSS 8.8)

Description

In the Linux kernel, the following vulnerability has been resolved: s390/vfio-ap: Fix hot-unplug skipped when last AP adapter or domain removed The vfio_ap_mdev_hot_unplug_cfg() function uses the return value of bitmap_andnot() to determine whether the guest APCB needs to be updated. However, bitmap_andnot() returns false when the resulting destination bitmap is empty. This means that if the only adapter, domain or control domain assigned to an mdev is removed from the host's AP configuration, the bit is correctly cleared from the shadow APCB, but bitmap_andnot() returns false because the result is an empty bitmap. Consequently, do_hotplug remains 0 and vfio_ap_mdev_update_guest_apcb() is never called, leaving the KVM guest with stale hardware access to the unplugged AP devices. Fix this by replacing the bitmap_andnot() return value check with bitmap_intersects() to determine whether the shadow APCB actually overlaps with the removal mask. If there is an intersection, call bitmap_andnot() solely for its side effect of clearing the bits, then unconditionally set do_hotplug to trigger the guest APCB update.

Metrics

CVSS 3.1

8.8/10

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= eeb386aeb5b7c8d2dae6a3ba49255d8a97803182, < f58e824de8577fe411f6199d659731a0f86a7275; >= eeb386aeb5b7c8d2dae6a3ba49255d8a97803182, < 3a9b049bbdc40165d7f3e20b818eec95e5694d96; >= eeb386aeb5b7c8d2dae6a3ba49255d8a97803182, < 753aa3bb1273bc0d36adb013d5915cc8ff6b72a9; >= eeb386aeb5b7c8d2dae6a3ba49255d8a97803182, < c45753c32d452d10d8efaeb52587e9e6e8126e33; >= eeb386aeb5b7c8d2dae6a3ba49255d8a97803182, < 04b35dd88c108b2d2ceaaa396aba1cb4049d5831; >= eeb386aeb5b7c8d2dae6a3ba49255d8a97803182, < 917f509bfb88048094dbb85c4e9dbc4d6fe4a886
Linux	Linux	6.0

References

Timeline

Published: Sep 16, 2026
Last Modified: Sep 16, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-89957?

In the Linux kernel, the following vulnerability has been resolved: s390/vfio-ap: Fix hot-unplug skipped when last AP adapter or domain removed The vfio_ap_mdev_hot_unplug_cfg() function uses the return value of bitmap_andnot() to determine whether the guest APCB needs to be updated. However, bitmap_andnot() returns false when the resulting destination bitmap is empty. This means that if the only adapter, domain or control domain assigned to an mdev is removed from the host's AP configuration, the bit is correctly cleared from the shadow APCB, but bitmap_andnot() returns false because the result is an empty bitmap. Consequently, do_hotplug remains 0 and vfio_ap_mdev_update_guest_apcb() is never called, leaving the KVM guest with stale hardware access to the unplugged AP devices. Fix this by replacing the bitmap_andnot() return value check with bitmap_intersects() to determine whether the shadow APCB actually overlaps with the removal mask. If there is an intersection, call bitmap_andnot() solely for its side effect of clearing the bits, then unconditionally set do_hotplug to trigger the guest APCB update.

How severe is CVE-2026-89957?

CVE-2026-89957 has a CVSS score of 8.8/10 (HIGH severity).

How do I fix CVE-2026-89957?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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