# CVE-2026-64561: KVM: x86: Check for invalid/obsolete root *after* making MMU pages available

> A race condition in KVM's shadow MMU allows mapping memory into invalid roots, potentially causing system crashes or arbitrary code execution.

- **Severity:** High 8.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/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:** 4 Aug 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-94368, BELL-CVE-2026-64561, DEBIAN-CVE-2026-64561, GHSA-hp26-g45f-hxp5, OESA-2026-3709, UBUNTU-CVE-2026-64561

## What is CVE-2026-64561?

CVE-2026-64561 is a high-severity vulnerability in Linux, published on 4 Aug 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: Check for invalid/obsolete root *after* making MMU pages available

Check for a "stale" page fault, i.e. for an invalid and/or obsolete root,
after making MMU pages available for the shadow MMU.  If reclaiming shadow
pages zaps an in-use root, i.e. marks it invalid, then KVM will attempt to
map memory into an invalid root.  On its own, populating an invalid root is
"fine", but because child shadow pages inherit their parent's role, any
children created during the map/fetch will be created as invalid pages,
thus violating KVM's invariant that invalid pages are never on the list of
active MMU pages.

Note, the underlying flaw has existed since KVM first started tracking
invalid roots in 2008 (commit 2e53d63acba7, "KVM: MMU: ignore zapped root
pagetables"), but the true badness only came along in 2020 (Linux 5.9)
with the invariant that invalid shadow pages can't be on the list of
active pages.

Note #2, inheriting role.invalid when creating child shadow pages is also
far from ideal; that flaw will be addressed separately.

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2026-64561?


## How do I fix CVE-2026-64561?

Apply the vendor's patch.

## Is CVE-2026-64561 being exploited?

There is no known exploitation of CVE-2026-64561 in the wild and no public exploit code.

Public exploit code:

- CVE-2026-64561 (github_poc): https://github.com/HORKimhab/CVE-2026-64561
- Guest-to-host KVM/x86 escape exploiting CVE-2026-64561, delivering a full PoC chain and analysis for security researchers. (github_poc): https://github.com/aarif450/Zapscape
- Zapscape (CVE-2026-64561) KVM/x86 shadow MMU UAF guest-to-host escape PoC mirror — V4bel/@v4bel, MIT; for authorized security testing (github_poc): https://github.com/HackSpeak/CVE-2026-64561
- Generic kernel live patch for the KVM/x86 shadow-MMU use-after-free (Zapscape, CVE-2026-64561) (github_poc): https://github.com/Aoripus-LTD/Zapscape-Fix
- Tracking Zapscape (CVE-2026-64561), the KVM/x86 shadow-MMU guest-to-host escape (github_poc): https://github.com/suominen/zapscape
- Exploit KVM/x86 guest-to-host escape CVE-2026-64561 with Zapscape, a proof-of-concept demonstrating hypervisor vulnerability. (github_poc): https://github.com/aarif450/aarif450.github.io

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64561 and fix it if it is affected.

What it is: CVE-2026-64561 is a high-severity vulnerability in Linux, published on 4 Aug 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-2026-64561 in the wild and no public exploit code.

Affected product: Linux. 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-2026-64561/ (Markdown: https://insights.sbomify.com/CVE-2026-64561/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64561
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64561
- OSV: https://osv.dev/vulnerability/CVE-2026-64561

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64561/
Summaries are generated and may contain mistakes; the official description above is the record.