# CVE-2026-52944

## Summary

- **CVE ID:** CVE-2026-52944
- **Severity:** MEDIUM
- **CVSS Score:** 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H)
- **CWE:** N/A
- **Published:** Jun 24, 2026
- **Last Modified:** Sep 14, 2026

## 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.

## Affected Products

- Linux — Linux (e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9)
- Linux — Linux (5.15)
- Linux — Linux (0)
- Linux — Linux (6.6.143)
- Linux — Linux (6.18.35)
- Linux — Linux (7.0.12)
- Linux — Linux (7.1)
- Linux — Linux (5.15.221)
- Linux — Linux (6.1.188)
- Linux — Linux (6.12.110)

## References

- [CNA](https://git.kernel.org/stable/c/3127a884525dc8ca4def73254bfcd3ccef0bf812)
- [CNA](https://git.kernel.org/stable/c/de9eb0b44fa9123170e6245b49638e0e453c10f8)
- [CNA](https://git.kernel.org/stable/c/aef151bcfa494bfe983669de2726734b534adb73)
- [CNA](https://git.kernel.org/stable/c/cc57232cae23c0df91b4a59d0f519141ce9b5b02)
- [CNA](https://git.kernel.org/stable/c/ef664475c1bf1a27d45dae6848ca9c9c4d86853f)
- [CNA](https://git.kernel.org/stable/c/3a9a0a1c38ef90788f5d7c4b29903c8b220f744a)
- [CNA](https://git.kernel.org/stable/c/c5ab11263e3c89aa7989afc5374ef7743e092fd0)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.12%
- **EPSS Percentile:** 2.2

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._