# CVE-2026-64390: ksmbd: track the connection owning a byte-range lock

> A use-after-free vulnerability in the Linux kernel's ksmbd module allows attackers to execute arbitrary code or cause a denial of service via SMB multichannel operations.

- **Severity:** High 8.8 (`CVSS:3.1/AV:N/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:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Jul 2026
- **Updated:** 17 Aug 2026
- **Also known as:** BELL-CVE-2026-64390, DEBIAN-CVE-2026-64390, GHSA-pgh2-g34p-4j6m, ROOT-OS-DEBIAN-12-CVE-2026-64390, ROOT-OS-DEBIAN-13-CVE-2026-64390, ROOT-OS-UBUNTU-2204-CVE-2026-64390, UBUNTU-CVE-2026-64390

## What is CVE-2026-64390?

CVE-2026-64390 is a high-severity use after free vulnerability in Linux kernel, published on 25 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: track the connection owning a byte-range lock

SMB2_LOCK adds each granted byte-range lock to both the file lock list
and the lock list of the connection which handled the request.  The
final close and durable handle paths, however, remove the connection
list entry while holding fp->conn->llist_lock.

With SMB3 multichannel, the connection handling the LOCK request can be
different from the connection which opened the file.  The entry can
therefore be removed under a different spinlock from the one protecting
the list it belongs to.  A concurrent traversal can then access freed
struct ksmbd_lock and struct file_lock objects.

Record the connection owning each lock's clist entry and hold a
reference to it while the entry is linked.  Use that connection and its
llist_lock for unlock, rollback, close, and durable preserve.  Durable
reconnect assigns the new connection as the owner when publishing the
locks again.

## Which versions are affected by CVE-2026-64390?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-64390?

Apply the vendor's patch.

## Is CVE-2026-64390 being exploited?

There is no known exploitation of CVE-2026-64390 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-2026-64390 and fix it if it is affected.

What it is: CVE-2026-64390 is a high-severity use after free vulnerability in Linux kernel, published on 25 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-64390 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-2026-64390/ (Markdown: https://insights.sbomify.com/CVE-2026-64390/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64390
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64390
- OSV: https://osv.dev/vulnerability/CVE-2026-64390

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64390/
Summaries are generated and may contain mistakes; the official description above is the record.