# CVE-2023-53663: KVM: nSVM: Check instead of asserting on nested TSC scaling support

> A local attacker with userspace access can trigger a kernel warning and potential denial of service in KVM nested SVM by manipulating TSC scaling features.

- **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:** 7 Oct 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2023-53663, DEBIAN-CVE-2023-53663, GHSA-92f6-rh29-hfq6, UBUNTU-CVE-2023-53663

## What is CVE-2023-53663?

CVE-2023-53663 is a medium-severity denial of service vulnerability in Linux kernel, published on 7 Oct 2025. 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: nSVM: Check instead of asserting on nested TSC scaling support

Check for nested TSC scaling support on nested SVM VMRUN instead of
asserting that TSC scaling is exposed to L1 if L1's MSR_AMD64_TSC_RATIO
has diverged from KVM's default.  Userspace can trigger the WARN at will
by writing the MSR and then updating guest CPUID to hide the feature
(modifying guest CPUID is allowed anytime before KVM_RUN).  E.g. hacking
KVM's state_test selftest to do

		vcpu_set_msr(vcpu, MSR_AMD64_TSC_RATIO, 0);
		vcpu_clear_cpuid_feature(vcpu, X86_FEATURE_TSCRATEMSR);

after restoring state in a new VM+vCPU yields an endless supply of:

  ------------[ cut here ]------------
  WARNING: CPU: 164 PID: 62565 at arch/x86/kvm/svm/nested.c:699
           nested_vmcb02_prepare_control+0x3d6/0x3f0 [kvm_amd]
  Call Trace:
   <TASK>
   enter_svm_guest_mode+0x114/0x560 [kvm_amd]
   nested_svm_vmrun+0x260/0x330 [kvm_amd]
   vmrun_interception+0x29/0x30 [kvm_amd]
   svm_invoke_exit_handler+0x35/0x100 [kvm_amd]
   svm_handle_exit+0xe7/0x180 [kvm_amd]
   kvm_arch_vcpu_ioctl_run+0x1eab/0x2570 [kvm]
   kvm_vcpu_ioctl+0x4c9/0x5b0 [kvm]
   __se_sys_ioctl+0x7a/0xc0
   __x64_sys_ioctl+0x21/0x30
   do_syscall_64+0x41/0x90
   entry_SYSCALL_64_after_hwframe+0x63/0xcd
  RIP: 0033:0x45ca1b

Note, the nested #VMEXIT path has the same flaw, but needs a different
fix and will be handled separately.

## Which versions are affected by CVE-2023-53663?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2023-53663?

Apply the vendor's patch.

## Is CVE-2023-53663 being exploited?

There is no known exploitation of CVE-2023-53663 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-2023-53663 and fix it if it is affected.

What it is: CVE-2023-53663 is a medium-severity denial of service vulnerability in Linux kernel, published on 7 Oct 2025. 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-2023-53663 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-2023-53663/ (Markdown: https://insights.sbomify.com/CVE-2023-53663/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-53663
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-53663
- OSV: https://osv.dev/vulnerability/CVE-2023-53663

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-53663/
Summaries are generated and may contain mistakes; the official description above is the record.