# CVE-2026-68093: KVM: SVM: Bump asid_generation on CPU online to avoid ASID collision after hotplug

> A race condition in KVM SVM allows ASID collisions after CPU hotplug, leading to stale TLB entries, potential data leakage between VMs, or denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 10 Aug 2026
- **Updated:** 19 Aug 2026
- **Also known as:** BELL-CVE-2026-68093, DEBIAN-CVE-2026-68093, GHSA-99gx-mqgq-5pqg, UBUNTU-CVE-2026-68093

## What is CVE-2026-68093?

CVE-2026-68093 is a vulnerability in Linux, published on 10 Aug 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: Bump asid_generation on CPU online to avoid ASID collision after hotplug

If a vCPU stays scheduled out (or blocked) while the last pCPU it ran
on goes through a hotplug cycle (online->offline->online), and the vCPU
then resumes execution on the same pCPU, then it is possible for it to
run with an ASID that has now been assigned to a different vCPU,
resulting in stale TLB translations being used.

svm_enable_virtualization_cpu() resets asid_generation to 1 and sets
next_asid to max_asid + 1 on every CPU online event, including hotplug
cycles.  Because next_asid starts beyond the pool boundary, the first
call to new_asid() after an online event always wraps the pool,
incrementing asid_generation to 2 and assigning ASIDs starting from
min_asid.

Consider two vCPUs from different VMs, vCPU-A pinned to CPU-X holding
asid_generation=2 and ASID=N from before the hotplug event:

  1. CPU-X goes offline and back online: asid_generation resets to 1,
     next_asid = max_asid + 1.

  2. One or more vCPUs migrate to CPU-X and call new_asid(), wrapping
     the pool and consuming ASIDs starting from min_asid.  Eventually
     vCPU-B from a different VM is assigned asid_generation=2, ASID=N
     — the same ASID that vCPU-A held before the hotplug.

  3. vCPU-A enters pre_svm_run() on CPU-X: current_vmcb->cpu is
     unchanged so the migration branch is skipped.  Its saved
     asid_generation=2 matches sd->asid_generation=2, so the generation
     check silently passes and vCPU-A continues running with ASID=N —
     the same ASID just freshly assigned to vCPU-B.

Both vCPUs from different VMs now run on CPU-X with the same ASID,
causing them to share NPT TLB entries and producing stale translations.

The collision manifests as a KVM internal error (Suberror: 1, emulation
failure).  The NPT page fault reports a faulting GPA far outside the
VM's physical memory range — a sign of stale TLB translations being
used.  KVM falls back to instruction emulation, which fails on
FPU/XSave instructions (XRSTOR, STMXCSR) that the emulator does not
implement.

Fix this by incrementing asid_generation instead of resetting it to 1
in svm_enable_virtualization_cpu().  On module load, asid_generation
starts at 0 (memset) and the increment produces 1, identical to the
old behaviour.  On subsequent hotplug cycles the generation advances
beyond any value a vCPU previously observed on this CPU, so the
generation check in pre_svm_run() reliably forces new_asid() on every
vCPU after every hotplug cycle.

## Which versions are affected by CVE-2026-68093?


## How do I fix CVE-2026-68093?

Apply the vendor's patch.

## Is CVE-2026-68093 being exploited?

There is no known exploitation of CVE-2026-68093 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-68093 and fix it if it is affected.

What it is: CVE-2026-68093 is a vulnerability in Linux, published on 10 Aug 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-2026-68093 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-2026-68093/ (Markdown: https://insights.sbomify.com/CVE-2026-68093/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-68093
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-68093
- OSV: https://osv.dev/vulnerability/CVE-2026-68093

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-68093/
Summaries are generated and may contain mistakes; the official description above is the record.