# CVE-2026-31444: ksmbd: fix use-after-free and NULL deref in smb_grant_oplock()

> A use-after-free and NULL dereference in the Linux kernel ksmbd module allows attackers to cause denial of service or potentially execute code.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 22 Apr 2026
- **Updated:** 5 Aug 2026
- **Also known as:** AZL-83324, BELL-CVE-2026-31444, DEBIAN-CVE-2026-31444, GHSA-8vw8-r4jr-vp93, UBUNTU-CVE-2026-31444

## What is CVE-2026-31444?

CVE-2026-31444 is a critical use after free vulnerability in Linux kernel, published on 22 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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

ksmbd: fix use-after-free and NULL deref in smb_grant_oplock()

smb_grant_oplock() has two issues in the oplock publication sequence:

1) opinfo is linked into ci->m_op_list (via opinfo_add) before
   add_lease_global_list() is called.  If add_lease_global_list()
   fails (kmalloc returns NULL), the error path frees the opinfo
   via __free_opinfo() while it is still linked in ci->m_op_list.
   Concurrent m_op_list readers (opinfo_get_list, or direct iteration
   in smb_break_all_levII_oplock) dereference the freed node.

2) opinfo->o_fp is assigned after add_lease_global_list() publishes
   the opinfo on the global lease list.  A concurrent
   find_same_lease_key() can walk the lease list and dereference
   opinfo->o_fp->f_ci while o_fp is still NULL.

Fix by restructuring the publication sequence to eliminate post-publish
failure:

- Set opinfo->o_fp before any list publication (fixes NULL deref).
- Preallocate lease_table via alloc_lease_table() before opinfo_add()
  so add_lease_global_list() becomes infallible after publication.
- Keep the original m_op_list publication order (opinfo_add before
  lease list) so concurrent opens via same_client_has_lease() and
  opinfo_get_list() still see the in-flight grant.
- Use opinfo_put() instead of __free_opinfo() on err_out so that
  the RCU-deferred free path is used.

This also requires splitting add_lease_global_list() to take a
preallocated lease_table and changing its return type from int to void,
since it can no longer fail.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-31444?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31444?

Apply the vendor's patch.

## Is CVE-2026-31444 being exploited?

There is no known exploitation of CVE-2026-31444 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-2026-31444 and fix it if it is affected.

What it is: CVE-2026-31444 is a critical use after free vulnerability in Linux kernel, published on 22 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-31444 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-2026-31444/ (Markdown: https://insights.sbomify.com/CVE-2026-31444/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31444
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31444
- OSV: https://osv.dev/vulnerability/CVE-2026-31444

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31444/
Summaries are generated and may contain mistakes; the official description above is the record.