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Fencer Vulns
medium 5.5

CVE-2026-43265 json

KVM: x86: Ignore -EBUSY when checking nested events from vcpu_block()

published 2026-05-06 6 mo ago modified 2026-11-06 2 d ago also EUVD-2026-27662

cvss
5.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.1%
EPSS 0.1% chance of exploitation in 30 days, percentile 1%
public exploits
0
none known

Summary

In the Linux kernel, the following vulnerability has been resolved:

KVM: x86: Ignore -EBUSY when checking nested events from vcpu_block()

Ignore -EBUSY when checking nested events after exiting a blocking state while L2 is active, as exiting to userspace will generate a spurious userspace exit, usually with KVM_EXIT_UNKNOWN, and likely lead to the VM's demise. Continuing with the wakeup isn't perfect either, as *something* has gone sideways if a vCPU is awakened in L2 with an injected event (or worse, a nested run pending), but continuing on gives the VM a decent chance of surviving without any major side effects.

As explained in the Fixes commits, it _should_ be impossible for a vCPU to be put into a blocking state with an already-injected event (exception, IRQ, or NMI). Unfortunately, userspace can stuff MP_STATE and/or injected events, and thus put the vCPU into what should be an impossible state.

Don't bother trying to preserve the WARN, e.g. with an anti-syzkaller Kconfig, as WARNs can (hopefully) be added in paths where _KVM_ would be violating x86 architecture, e.g. by WARNing if KVM attempts to inject an exception or interrupt while the vCPU isn't running.

Patch / fix

  • Linux Linux 6.1.167, 6.6.130, 6.12.77, 6.18.17, 6.19.6, 7.0
  • linux Debian 12 6.1.170-1
  • linux Debian 13 6.12.85-1
  • linux Debian 14 6.19.6-1

debian advisories DEBIAN-CVE-2026-43265

  • linux Ubuntu 24.04 LTS 6.8.0-136.136
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1061.64
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1064.72
  • linux-gke Ubuntu 24.04 LTS 6.8.0-1059.67
  • linux-ibm Ubuntu 24.04 LTS 6.8.0-1061.62
  • linux-azure Ubuntu 24.04 LTS 6.8.0-1063.71
  • linux-gkeop Ubuntu 24.04 LTS 6.8.0-1046.50
  • linux-raspi Ubuntu 24.04 LTS 6.8.0-1061.65

ubuntu advisories UBUNTU-CVE-2026-43265

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel-64kb SLE Module for Basesystem 15 SP7 6.4.0-150700.53.55.1
  • kernel-syms SLE Module for Development Tools 15 SP7 6.4.0-150700.53.55.1
  • kernel-azure SLE Module for Public Cloud 15 SP7 6.4.0-150700.53.55.1
  • kernel-source SLE Module for Development Tools 15 SP7, SLE Module for Basesystem 15 SP7 6.4.0-150700.53.55.1
  • kernel-default SLE Workstation Extension 15 SP7, SLE Module for Legacy 15 SP7, SLE Module for Basesystem 15 SP7 +2 more 6.4.0-150700.53.55.1
  • kernel-zfcpdump SLE Module for Basesystem 15 SP7 6.4.0-150700.53.55.1
  • kernel-obs-build SLE Module for Development Tools 15 SP7 6.4.0-150700.53.55.1
  • kernel-default-base SLE Module for Basesystem 15 SP7 6.4.0-150700.53.55.1.150700.17.33.1

suse advisories SUSE-SU-2026:2238-1SUSE-SU-2026:21834-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-43265 updated cvss 5.5

kernel: KVM: x86: Ignore -EBUSY when checking nested events from vcpu_block()

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more
    affected: no fix available, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 10 kernel
    affected: no fix available “Fix deferred”
  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
2 d ago

Exploit prediction

0.12% chance of exploitation in the next 30 days, higher than 1% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux

Classification

Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.