# CVE-2026-52944: ksmbd: fix FSCTL permission bypass by adding a permission check for FSCTL_SET_SPARSE

> Attackers can bypass read-only share restrictions and modify file sparse attributes without proper write permissions in the Linux kernel ksmbd module.

- **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:** 24 Jun 2026
- **Updated:** 14 Sep 2026
- **Also known as:** BELL-CVE-2026-52944, DEBIAN-CVE-2026-52944, GHSA-v762-vr2v-9263, ROOT-OS-DEBIAN-12-CVE-2026-52944, ROOT-OS-DEBIAN-13-CVE-2026-52944, ROOT-OS-UBUNTU-2204-CVE-2026-52944, ROOT-OS-UBUNTU-2404-CVE-2026-52944, UBUNTU-CVE-2026-52944

## What is CVE-2026-52944?

CVE-2026-52944 is a medium-severity missing authorization vulnerability in Linux kernel, published on 24 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 FSCTL permission bypass by adding a permission check for FSCTL_SET_SPARSE

FSCTL_SET_SPARSE in fsctl_set_sparse() modifies the file's sparse
attribute and saves it through xattr without any permission checks.

This exposes two issues:

1) A client on a read-only share can change the sparse attribute
   on files it opened, even though the share is read-only.
   Other FSCTL write operations already check
   test_tree_conn_flag(work->tcon, KSMBD_TREE_CONN_FLAG_WRITABLE),
   but FSCTL_SET_SPARSE does not.

2) Even on writable shares, clients without FILE_WRITE_DATA or
   FILE_WRITE_ATTRIBUTES access should not modify the sparse
   attribute. Similar handle-level checks exist in other functions
   but are missing here.

Add both share-level writable check and per-handle access check.
Use goto out on error to avoid leaking file references.

## Which versions are affected by CVE-2026-52944?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-52944?

Apply the vendor's patch.

## Is CVE-2026-52944 being exploited?

There is no known exploitation of CVE-2026-52944 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-2026-52944 and fix it if it is affected.

What it is: CVE-2026-52944 is a medium-severity missing authorization vulnerability in Linux kernel, published on 24 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-2026-52944 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-2026-52944/ (Markdown: https://insights.sbomify.com/CVE-2026-52944/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-52944
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-52944
- OSV: https://osv.dev/vulnerability/CVE-2026-52944

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-52944/
Summaries are generated and may contain mistakes; the official description above is the record.