# CVE-2026-98715: KVM: SVM: Preserve TLB control (i.e. pending TLB flush) on failed VMRUN

> A guest VM can trigger unnecessary TLB flushes on the host, causing performance degradation and potential denial of service for other virtual machines.

- **Severity:** Not scored
- **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:** 18 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-108773, BELL-CVE-2026-98715, DEBIAN-CVE-2026-98715, GHSA-j396-gv6v-75wx, UBUNTU-CVE-2026-98715

## What is CVE-2026-98715?

CVE-2026-98715 is a denial of service vulnerability in Linux, published on 18 Oct 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: SVM: Preserve TLB control (i.e. pending TLB flush) on failed VMRUN

Don't reset the VMCB's TLB control back to "do nothing" on a failed VMRUN,
as empirical testing shows that the CPU performs the requested TLB flush if
and only if VMRUN is successful, i.e. clearing TLB control on a failed
VMRUN effectively drops a TLB flush.

Explicitly track the need to flush all ASIDs on a per-CPU basis, as the
ASID reuse condition is tied to the pCPU, not to the vCPU.  As a bonus,
this also obviates the need to avoid clobbering FLUSH_ALL_ASID with
TLB_CONTROL_FLUSH_ASID, e.g. in svm_flush_tlb_asid().

Deliberately don't bother saving/restoring the "old" tlb_ctl on failure,
in quotes because it's not exactly the old tlb_ctl, it's the tlb_ctl from
after pre_svm_run(), but before updating tlb_ctl for flush_all_asids.  If
VMRUN fails and TLB_CONTROL_FLUSH_ALL_ASID is forced, then the next
successful run of the VMCB *may* unnecessarily flush all ASIDs, which
strictly speaking could result in noisy neighbor issues.  However, the
fact that new_asid() is already guest-triggerable, because of KVM's flawed
behavior of clearing the ASID on emulated INIT, means that a guest can
already trigger a flush of all ASIDs at roughly the same rate.  And once
KVM stops clobbering the ASID on emulated INIT, *or* assigns a static ASID
to each vCPU, this flaw goes away.

## Which versions are affected by CVE-2026-98715?


## How do I fix CVE-2026-98715?

Apply the vendor's patch.

## Is CVE-2026-98715 being exploited?

There is no known exploitation of CVE-2026-98715 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98715 and fix it if it is affected.

What it is: CVE-2026-98715 is a denial of service vulnerability in Linux, published on 18 Oct 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-2026-98715 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-2026-98715/ (Markdown: https://insights.sbomify.com/CVE-2026-98715/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98715
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98715
- OSV: https://osv.dev/vulnerability/CVE-2026-98715

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98715/
Summaries are generated and may contain mistakes; the official description above is the record.