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CVE-2026-64562
KVM: nVMX: Hide shadow VMCS right after VMCLEAR
Published 2026-08-04 (2 months ago) by the Linux kernel CNA. Subsystem arch/x86. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-64562 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixedDLA-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6415-1 · 2026-08-06 · text | 6.12.101-1 | Update the kernel and reboot. DSA-6415-1 shipped the fix on 2026-08-06, in 6.12.101-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.6-1 | Update the kernel and reboot. Fixed in 7.1.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.6-1 | Update the kernel and reboot. Fixed in 7.1.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4745-1 · 2026-08-18 · text | 6.12.101-1~deb12u1 | Update the kernel and reboot. DLA-4745-1 shipped the fix on 2026-08-18, in 6.12.101-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
free_nested() frees the shadow VMCS while vmcs01 still points to it. But because it is asynchronous with respect to loaded_vmcs_clear(), the vCPU might migrate before the pointer is cleared and __loaded_vmcs_clear() may then execute VMCLEAR. The VMCS needs to stay attached until its explicit VMCLEAR completes, but then it can be hidden and the page safely freed.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
arch/x86/kvm/vmx/nested.c
- What this is
- KERNEL VIRTUAL MACHINE FOR X86 (KVM/x86)MAINTAINERS section matched on arch/x86/kvm/*/ · kvm@vger.kernel.org · Supported
Show whether Debian builds this, per release
Not established. This site could not find the build rule for the affected file in the kernel trees Debian ships, so it has no answer about whether Debian compiles this code. Read that as unknown, never as absent.
- bookworm, trixie, forky, sid, bookworm · linux-6.12?
- ?
- not established - no Makefile entry for the affected file
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS
Signals
- Published
- 2026-08-04 (2 months ago)source
- CVSS
- 8.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.12%, higher than 2.0% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- arch/x86
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.9 | 5.10.265 | b82c3144d826 |
| 4.9 | 5.15.216 | 4f50e6aec16f |
| 4.9 | 6.1.183 | dc3eecfa219e |
| 4.9 | 6.6.148 | af56298e9d86 |
| 4.9 | 6.12.101 | 589419470030 |
| 4.9 | 6.18.42 | 8001d2ce9d9b |
| 4.9 | 7.1.6 | 1dabef6e2065 |
| 4.9 | 7.2 | 622ebfac01ba |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DLA-4745-1 | 2026-08-18 | bookworm 6.12.101-1~deb12u1 | tracker |
| DSA-6415-1 | 2026-08-06 | trixie 6.12.101-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The bug is reached through local KVM nested VMX: open /dev/kvm, run a nested guest, then tear down nested state (VMXOFF/handle_vmxoff or vmx_leave_nested). It is not reachable via network or adjacent-radio packets.
- AC:LAttack complexity, low
- A KVM VMM attacker controls both sides of the race by driving nested teardown (VMXOFF/vcpu destroy) while forcing vCPU migration via thread affinity/scheduling so __loaded_vmcs_clear() VMCLEARs the dangling shadow VMCS pointer.
- PR:LPrivileges required, low
- Exploitation needs permission to use /dev/kvm and nested VMX (commonly kvm-group or equivalent), not real init-namespace root; KVM create/run ioctls have no CAP_SYS_ADMIN gate on this path.
- UI:NUser interaction, none
- After the attacker has KVM/nested access, they trigger free_nested and migration themselves; no separate victim action is required.
- S:CScope, changed
- free_nested runs in host KVM while handling L1 nested VMX teardown, and the UAF corrupts host kernel memory, crossing the guest/hypervisor isolation boundary (guest-to-host escape class).
- C:HConfidentiality impact, high
- The dangling shadow VMCS pointer lets VMCLEAR operate on a freed page that may be reused, yielding a host kernel use-after-free that can be leveraged for arbitrary information disclosure.
- I:HIntegrity impact, high
- VMCLEAR writes VMCS state into the freed page; with page reuse this is host heap corruption enabling write primitives and potential host code execution, consistent with UAF guidance.
- A:HAvailability impact, high
- Use-after-free of the shadow VMCS page can oops/panic the host kernel when VMCLEAR or later accessors touch reallocated memory, fully denying host availability.