# CVE-2023-53208: KVM: nSVM: Load L1's TSC multiplier based on L1 state, not L2 state

> A flaw in Linux KVM allows triggering a kernel warning via nested virtualization, potentially causing a denial of service.

- **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:** 15 Sep 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2023-53208, DEBIAN-CVE-2023-53208, GHSA-2h47-q9f6-8gx7, UBUNTU-CVE-2023-53208

## What is CVE-2023-53208?

CVE-2023-53208 is a medium-severity denial of service vulnerability in Linux kernel, published on 15 Sep 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: Load L1's TSC multiplier based on L1 state, not L2 state

When emulating nested VM-Exit, load L1's TSC multiplier if L1's desired
ratio doesn't match the current ratio, not if the ratio L1 is using for
L2 diverges from the default.  Functionally, the end result is the same
as KVM will run L2 with L1's multiplier if L2's multiplier is the default,
i.e. checking that L1's multiplier is loaded is equivalent to checking if
L2 has a non-default multiplier.

However, the assertion that TSC scaling is exposed to L1 is flawed, as
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: 10 PID: 206939 at arch/x86/kvm/svm/nested.c:1105
           nested_svm_vmexit+0x6af/0x720 [kvm_amd]
  Call Trace:
   nested_svm_exit_handled+0x102/0x1f0 [kvm_amd]
   svm_handle_exit+0xb9/0x180 [kvm_amd]
   kvm_arch_vcpu_ioctl_run+0x1eab/0x2570 [kvm]
   kvm_vcpu_ioctl+0x4c9/0x5b0 [kvm]
   ? trace_hardirqs_off+0x4d/0xa0
   __se_sys_ioctl+0x7a/0xc0
   __x64_sys_ioctl+0x21/0x30
   do_syscall_64+0x41/0x90
   entry_SYSCALL_64_after_hwframe+0x63/0xcd

Unlike the nested VMRUN path, hoisting the svm->tsc_scaling_enabled check
into the if-statement is wrong as KVM needs to ensure L1's multiplier is
loaded in the above scenario.   Alternatively, the WARN_ON() could simply
be deleted, but that would make KVM's behavior even more subtle, e.g. it's
not immediately obvious why it's safe to write MSR_AMD64_TSC_RATIO when
checking only tsc_ratio_msr.

## Which versions are affected by CVE-2023-53208?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2023-53208?

Apply the vendor's patch.

## Is CVE-2023-53208 being exploited?

There is no known exploitation of CVE-2023-53208 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-2023-53208 and fix it if it is affected.

What it is: CVE-2023-53208 is a medium-severity denial of service vulnerability in Linux kernel, published on 15 Sep 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-2023-53208 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-2023-53208/ (Markdown: https://insights.sbomify.com/CVE-2023-53208/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-53208
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-53208
- OSV: https://osv.dev/vulnerability/CVE-2023-53208

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-53208/
Summaries are generated and may contain mistakes; the official description above is the record.