CVE-2026-43265

/// Technical description

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, a

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References