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

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2026-06-24 · Updated: 2026-09-14

## Affected

- Linux: version range not reported
- Linux: 5.15

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
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## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/ef664475c1bf1a27d45dae6848ca9c9c4d86853f
- https://git.kernel.org/stable/c/3a9a0a1c38ef90788f5d7c4b29903c8b220f744a
- https://git.kernel.org/stable/c/3127a884525dc8ca4def73254bfcd3ccef0bf812
- https://git.kernel.org/stable/c/c5ab11263e3c89aa7989afc5374ef7743e092fd0
- https://git.kernel.org/stable/c/de9eb0b44fa9123170e6245b49638e0e453c10f8
- https://git.kernel.org/stable/c/aef151bcfa494bfe983669de2726734b534adb73
- https://git.kernel.org/stable/c/cc57232cae23c0df91b4a59d0f519141ce9b5b02

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Page: https://cve.now/CVE-2026-52944
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