# CVE-2026-64247: KVM: x86: hyper-v: Bound the bank index when querying sparse banks

> A missing bounds check in KVM Hyper-V TLB flush handling allows out-of-bounds reads, potentially causing kernel crashes or information leaks.

- **Severity:** High 8.4 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/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:** 24 Jul 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-64247, DEBIAN-CVE-2026-64247, GHSA-2rqc-j7rg-xg47, ROOT-OS-UBUNTU-2204-CVE-2026-64247, UBUNTU-CVE-2026-64247

## What is CVE-2026-64247?

CVE-2026-64247 is a high-severity use after free vulnerability in Linux kernel, published on 24 Jul 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: hyper-v: Bound the bank index when querying sparse banks

When checking if a VP ID is included in a sparse bank set, explicitly check
that the ID can actually be contained in a sparse bank (the TLFS allows for
a maximum of 64 banks of 64 vCPUs each).  When handling a paravirtual TLB
flush for L2, the VP ID is copied verbatim from the enlightened VMCS,
without any bounds check, i.e. isn't guaranteed to be under the limit of
4096.

Failure to check the bounds of the VP ID leads to an out-of-bounds read
when testing the sparse bank, and super strictly speaking could lead to KVM
performing an unnecessary TLB flush for an L2 vCPU.

  ==================================================================
  BUG: KASAN: use-after-free in hv_is_vp_in_sparse_set+0x85/0x100 [kvm]
  Read of size 8 at addr ffff88811ba5f598 by task hyperv_evmcs/2802

  CPU: 12 UID: 1000 PID: 2802 Comm: hyperv_evmcs Not tainted 7.1.0-rc2 #7 PREEMPT
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
  Call Trace:
   <TASK>
   dump_stack_lvl+0x51/0x60
   print_report+0xcb/0x5d0
   kasan_report+0xb4/0xe0
   kasan_check_range+0x35/0x1b0
   hv_is_vp_in_sparse_set+0x85/0x100 [kvm]
   kvm_hv_flush_tlb+0xe9e/0x16c0 [kvm]
   kvm_hv_hypercall+0xe6b/0x1e60 [kvm]
   vmx_handle_exit+0x485/0x1b60 [kvm_intel]
   kvm_arch_vcpu_ioctl_run+0x22e3/0x5070 [kvm]
   kvm_vcpu_ioctl+0x5d0/0x10c0 [kvm]
   __x64_sys_ioctl+0x129/0x1a0
   do_syscall_64+0xb9/0xcf0
   entry_SYSCALL_64_after_hwframe+0x4b/0x53
  RIP: 0033:0x7f0e62d1a9bf
   </TASK>

  The buggy address belongs to the physical page:
  page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffffffffffffffff pfn:0x11ba5f
  flags: 0x4000000000000000(zone=1)
  raw: 4000000000000000 0000000000000000 00000000ffffffff 0000000000000000
  raw: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000000
  page dumped because: kasan: bad access detected

  Memory state around the buggy address:
   ffff88811ba5f480: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
   ffff88811ba5f500: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
  >ffff88811ba5f580: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                              ^
   ffff88811ba5f600: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
   ffff88811ba5f680: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
  ==================================================================
  Disabling lock debugging due to kernel taint

Opportunistically add a compile time assertion to ensure the maximum number
of sparse banks exactly matches the number of possible bits in the passed
in mask.

[sean: add KASAN splat, drop comment, add assert, massage changelog]

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-64247?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-64247?

Apply the vendor's patch.

## Is CVE-2026-64247 being exploited?

There is no known exploitation of CVE-2026-64247 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-2026-64247 and fix it if it is affected.

What it is: CVE-2026-64247 is a high-severity use after free vulnerability in Linux kernel, published on 24 Jul 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-2026-64247 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-2026-64247/ (Markdown: https://insights.sbomify.com/CVE-2026-64247/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64247
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64247
- OSV: https://osv.dev/vulnerability/CVE-2026-64247

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64247/
Summaries are generated and may contain mistakes; the official description above is the record.