---
id: CVE-2026-52944
title: >-
  ksmbd: fix FSCTL permission bypass by adding a permission check for
  FSCTL_SET_SPARSE
summary: >-
  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 sa…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 <
    ef664475c1bf1a27d45dae6848ca9c9c4d86853f
  - >-
    Linux >= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 <
    3a9a0a1c38ef90788f5d7c4b29903c8b220f744a
  - >-
    Linux >= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 <
    3127a884525dc8ca4def73254bfcd3ccef0bf812
  - >-
    Linux >= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 <
    c5ab11263e3c89aa7989afc5374ef7743e092fd0
  - >-
    Linux >= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 <
    de9eb0b44fa9123170e6245b49638e0e453c10f8
  - >-
    Linux >= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 <
    aef151bcfa494bfe983669de2726734b534adb73
  - >-
    Linux >= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 <
    cc57232cae23c0df91b4a59d0f519141ce9b5b02
  - Linux 5.15
published: '2026-06-24'
updated: '2026-09-14'
sourceUpdated: '2026-09-14T11:58:26.890Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-52944'
references:
  - url: 'https://git.kernel.org/stable/c/ef664475c1bf1a27d45dae6848ca9c9c4d86853f'
  - url: 'https://git.kernel.org/stable/c/3a9a0a1c38ef90788f5d7c4b29903c8b220f744a'
  - url: 'https://git.kernel.org/stable/c/3127a884525dc8ca4def73254bfcd3ccef0bf812'
  - url: 'https://git.kernel.org/stable/c/c5ab11263e3c89aa7989afc5374ef7743e092fd0'
  - url: 'https://git.kernel.org/stable/c/de9eb0b44fa9123170e6245b49638e0e453c10f8'
  - url: 'https://git.kernel.org/stable/c/aef151bcfa494bfe983669de2726734b534adb73'
  - url: 'https://git.kernel.org/stable/c/cc57232cae23c0df91b4a59d0f519141ce9b5b02'
tags:
  - cve.org
epss: 0.00173
epssPercentile: 0.05859
ingestedAt: '2026-09-14T15:23:07.457Z'
---

## Overview

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.

## Affected

- `Linux >= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 < ef664475c1bf1a27d45dae6848ca9c9c4d86853f`
- `Linux >= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 < 3a9a0a1c38ef90788f5d7c4b29903c8b220f744a`
- `Linux >= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 < 3127a884525dc8ca4def73254bfcd3ccef0bf812`
- `Linux >= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 < c5ab11263e3c89aa7989afc5374ef7743e092fd0`
- `Linux >= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 < de9eb0b44fa9123170e6245b49638e0e453c10f8`
- `Linux >= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 < aef151bcfa494bfe983669de2726734b534adb73`
- `Linux >= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 < cc57232cae23c0df91b4a59d0f519141ce9b5b02`
- `Linux 5.15`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.