# CVE-2026-53271: ksmbd: fix NULL-deref of opinfo->conn in oplock/lease break notifiers

> A remote attacker can cause a kernel crash in ksmbd by triggering a race condition during oplock or lease break notifications.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 25 Jun 2026
- **Updated:** 25 Jun 2026
- **Also known as:** BELL-CVE-2026-53271, DEBIAN-CVE-2026-53271, GHSA-hxmm-jmj9-253j, UBUNTU-CVE-2026-53271

## What is CVE-2026-53271?

CVE-2026-53271 is a medium-severity vulnerability in Linux kernel, published on 25 Jun 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:

ksmbd: fix NULL-deref of opinfo->conn in oplock/lease break notifiers

smb2_oplock_break_noti() and smb2_lease_break_noti() read opinfo->conn
into a local with neither READ_ONCE() nor a NULL check.  Both run from
oplock_break() after opinfo_get_list() has dropped ci->m_lock, so a
concurrent SMB2 LOGOFF (session_fd_check()) can set op->conn = NULL
under ci->m_lock within that window.  ksmbd_conn_r_count_inc(conn) then
writes through NULL at offset 0xc4 -- a remotely triggerable oops.

Guard both reads the way compare_guid_key() already does: read
opinfo->conn with READ_ONCE() and return early if it is NULL, before
allocating the work struct so nothing leaks.  A NULL conn means the
client is gone and the break is moot, so return 0; oplock_break() treats
that as success and runs the normal teardown.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2026-53271?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-53271?

Apply the vendor's patch.

## Is CVE-2026-53271 being exploited?

There is no known exploitation of CVE-2026-53271 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-2026-53271 and fix it if it is affected.

What it is: CVE-2026-53271 is a medium-severity vulnerability in Linux kernel, published on 25 Jun 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-2026-53271 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-2026-53271/ (Markdown: https://insights.sbomify.com/CVE-2026-53271/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-53271
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53271
- OSV: https://osv.dev/vulnerability/CVE-2026-53271

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-53271/
Summaries are generated and may contain mistakes; the official description above is the record.