# CVE-2026-89965: nvdimm/btt: reject an arena whose nfree is below the lane count

> An out-of-bounds write in the Linux kernel NVDIMM BTT driver allows attackers to cause memory corruption and potential code execution via a crafted arena.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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:** 16 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-101126, BELL-CVE-2026-89965, DEBIAN-CVE-2026-89965, GHSA-gj9w-7mfp-hc5m, UBUNTU-CVE-2026-89965

## What is CVE-2026-89965?

CVE-2026-89965 is a high-severity 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:

nvdimm/btt: reject an arena whose nfree is below the lane count

The BTT info block's nfree field, the number of reserve free blocks, is
read from the medium without validation.  btt_freelist_init() and
btt_rtt_init() size the per-lane freelist[] and rtt[] arrays by nfree,
but the I/O path indexes them by the lane from nd_region_acquire_lane(),
which is bounded by nd_region->num_lanes (ND_MAX_LANES), not by nfree.
A crafted or foreign arena whose nfree is below the lane count makes
freelist[lane]/rtt[lane] run past the allocation: an out-of-bounds write.

btt.rst documents the nlanes = min(nfree, num_cpus) invariant, which the
code does not currently honor: num_lanes is ND_MAX_LANES regardless of
nfree.  Reject an arena whose nfree is below num_lanes at discovery,
before the per-lane arrays are allocated, enforcing that invariant.

## Which versions are affected by CVE-2026-89965?


## How do I fix CVE-2026-89965?

Apply the vendor's patch.

## Is CVE-2026-89965 being exploited?

There is no known exploitation of CVE-2026-89965 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89965 and fix it if it is affected.

What it is: CVE-2026-89965 is a high-severity 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-2026-89965 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-2026-89965/ (Markdown: https://insights.sbomify.com/CVE-2026-89965/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89965
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89965
- OSV: https://osv.dev/vulnerability/CVE-2026-89965

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89965/
Summaries are generated and may contain mistakes; the official description above is the record.