# CVE-2026-89923: KVM: s390: Free guest debug data on vcpu destroy

> A memory leak in the Linux kernel's KVM s390 implementation allows local attackers to exhaust system memory by repeatedly creating and destroying virtual CPUs with active hardware breakpoints.

- **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:** 16 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-101465, BELL-CVE-2026-89923, DEBIAN-CVE-2026-89923, GHSA-69xh-7r26-q3mw, UBUNTU-CVE-2026-89923

## What is CVE-2026-89923?

CVE-2026-89923 is a memory corruption vulnerability in Linux, published on 16 Sep 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: s390: Free guest debug data on vcpu destroy

kvm_s390_clear_bp_data() is only called from
kvm_arch_vcpu_ioctl_set_guest_debug(), i.e. when user space changes or
disables debugging. A vCPU that is destroyed while hardware breakpoints
are still armed - the normal case when the VMM just exits or crashes -
leaks hw_bp_info, hw_wp_info and all old_data buffers, since generic KVM
frees the vCPU right after kvm_arch_vcpu_destroy().

That is bounded by MAX_BP_COUNT entries, so roughly 8 KiB per vCPU, but
it is unbounded over VM lifetimes. The allocations are
GFP_KERNEL_ACCOUNT, so the charge also outlives the exiting process and
pins dying memcgs.

Fix by clearing the debug data on vCPU destruction. Calling it
unconditionally is fine: struct kvm_vcpu is zero allocated, so for a vCPU
that never enabled debugging the counters are 0 and the pointers NULL.

## Which versions are affected by CVE-2026-89923?


## How do I fix CVE-2026-89923?

Apply the vendor's patch.

## Is CVE-2026-89923 being exploited?

There is no known exploitation of CVE-2026-89923 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89923 and fix it if it is affected.

What it is: CVE-2026-89923 is a memory corruption vulnerability in Linux, published on 16 Sep 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-2026-89923 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-2026-89923/ (Markdown: https://insights.sbomify.com/CVE-2026-89923/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89923
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89923
- OSV: https://osv.dev/vulnerability/CVE-2026-89923

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89923/
Summaries are generated and may contain mistakes; the official description above is the record.