# CVE-2026-43265: KVM: x86: Ignore -EBUSY when checking nested events from vcpu_block()

> A flaw in Linux KVM allows a malicious userspace to trigger a spurious exit, causing the virtual machine to crash and resulting in denial of service.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **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:** Yes
- **Published:** 6 May 2026
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2026-43265, DEBIAN-CVE-2026-43265, GHSA-p7j5-r5cq-h6qj, ROOT-OS-UBUNTU-2404-CVE-2026-43265, UBUNTU-CVE-2026-43265

## What is CVE-2026-43265?

CVE-2026-43265 is a medium-severity denial of service vulnerability in Linux kernel, published on 6 May 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:

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.

## Which versions are affected by CVE-2026-43265?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-43265?

Apply the vendor's patch.

## Is CVE-2026-43265 being exploited?

There is no known exploitation of CVE-2026-43265 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-43265 and fix it if it is affected.

What it is: CVE-2026-43265 is a medium-severity denial of service vulnerability in Linux kernel, published on 6 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-43265 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-43265/ (Markdown: https://insights.sbomify.com/CVE-2026-43265/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43265
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43265
- OSV: https://osv.dev/vulnerability/CVE-2026-43265

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43265/
Summaries are generated and may contain mistakes; the official description above is the record.