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Linux Kernel EUVDEUVD-2026-27662

| CVE-2026-43265 MEDIUM
2026-05-06 Linux GHSA-p7j5-r5cq-h6qj
Code Injection Linux Red Hat Suse
5.5
CVSS 3.1 · NVD
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Severity by source

NVD PRIMARY
5.5 MEDIUM
AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
SUSE
MEDIUM
qualitative
Red Hat
5.5 LOW
qualitative

Primary rating from NVD.

CVSS VectorNVD

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Lifecycle Timeline

4
Analysis Generated
May 08, 2026 - 20:37 vuln.today
CVSS changed
May 08, 2026 - 20:37 NVD
5.5 (MEDIUM)
Patch available
May 06, 2026 - 13:32 EUVD
CVE Published
May 06, 2026 - 11:28 nvd
MEDIUM 5.5

DescriptionCVE.org

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.

AnalysisAI

Denial of service in Linux kernel KVM x86 nested virtualization allows local privileged attackers to crash virtual machines by manipulating vCPU state through userspace MP_STATE and injected event stuffing. When a vCPU is awakened from a blocking state in L2 (nested guest mode) with an already-injected event, the kernel generates spurious KVM_EXIT_UNKNOWN exits that typically terminate the VM. The vulnerability stems from insufficient validation of impossible vCPU states that userspace can artificially create, despite architectural safeguards that should prevent injected events during blocking. CVSS 5.5 (local, low complexity, high availability impact); EPSS 0.02% indicates minimal widespread exploitation likelihood.

Technical ContextAI

This vulnerability exists in KVM (Kernel-based Virtual Machine) x86 nested virtualization support, specifically in the vcpu_block() exit path when processing nested events for L2 (nested guest) execution. The root cause involves race condition handling and insufficient input validation in the nested event checking logic. When userspace directly manipulates vCPU state via KVM_SET_VCPU_EVENTS and KVM_SET_MP_STATE IOCTLs, it can create architecturally impossible states where a vCPU has both a blocking flag and an injected event simultaneously. The kernel's vcpu_block() function, upon wakeup, attempts to check for pending nested events but receives -EBUSY, indicating the vCPU cannot process events in its current state. Rather than handling this gracefully, the original code would exit to userspace with KVM_EXIT_UNKNOWN, destabilizing the guest VM. The fix involves ignoring the -EBUSY error and continuing execution, accepting that recovery is imperfect but preferable to immediate VM termination. CWE is not formally assigned but relates to improper input validation and race conditions in state management.

RemediationAI

Upgrade Linux kernel to patched stable versions: 6.1.167 or later for 6.1.x, 6.6.130 or later for 6.6.x, 6.12.77 or later for 6.12.x, 6.18.17 or later for 6.18.x, 6.19.6 or later for 6.19.x, or 7.0 and later for newer releases. Patches are available via git.kernel.org stable branches (referenced commits 78265cd066d73a5cb41c088fcae4a2515e480d97 for 6.6, ec3be7dc9391085a2d96700e159d66d1328b7ff6 for 6.1, and corresponding commits for other branches). The fix involves modifying the KVM x86 nested event handling code to ignore -EBUSY errors after vcpu_block() wakeup instead of exiting to userspace. As an interim compensating control, restrict direct vCPU state manipulation via KVM IOCTLs (KVM_SET_VCPU_EVENTS, KVM_SET_MP_STATE) to trusted userspace processes; this is typically default behavior in production hypervisors where QEMU/libvirt run as dedicated unprivileged users, but isolation may need verification in multi-tenant environments. This control does not fully mitigate the vulnerability but reduces attack surface if userspace is not fully trusted. Monitor for unexpected KVM_EXIT_UNKNOWN messages in hypervisor logs, which may indicate either exploitation attempts or genuine system faults.

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Vendor StatusVendor

SUSE

Severity: Medium
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Fixed
SUSE Linux Enterprise Desktop 15 SP7 Fixed
SUSE Linux Enterprise High Availability Extension 15 SP7 Fixed
SUSE Linux Enterprise High Availability Extension 15 SP7 Fixed
SUSE Linux Enterprise High Performance Computing 15 SP7 Fixed

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EUVD-2026-27662 vulnerability details – vuln.today
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