CVE-2026-89957 s390/vfio-ap: Fix hot-unplug skipped when last AP adapter or domain removed
A logic error in the Linux kernel vfio-ap driver allows KVM guests to retain stale access to unplugged AP devices, potentially exposing sensitive data.
- 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-2026-89957?
CVE-2026-89957 is a high-severity 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:
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.
Which versions are affected by CVE-2026-89957?
How do I fix CVE-2026-89957?
Apply the vendor's patch.
Is CVE-2026-89957 being exploited?
There is no known exploitation of CVE-2026-89957 in the wild and no public exploit code.
Sources
Also known as AZL-101433, BELL-CVE-2026-89957, DEBIAN-CVE-2026-89957, GHSA-pgcj-5wj3-jcmr, UBUNTU-CVE-2026-89957.