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

CVE-2026-52944 is fixed in 2 products on 1 platform, first by DEBIAN-CVE-2026-52944, released June 25, 2026. It is not reported as exploited. Patch Radar priority: Urgent.

- Web page: https://patchblox.com/security/cve/CVE-2026-52944
- Priority: Urgent
- CVSS: 9.8 (Critical)
- EPSS: 0.0012
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jun 24, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-52944

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 6.1.190-1 | [DEBIAN-CVE-2026-52944](https://patchblox.com/security/data/fix/linux/debian-cve-2026-52944.md) | Jun 25, 2026 |
| Linux | linux Debian 13.5 (trixie) | 6.12.111-1 | [DEBIAN-CVE-2026-52944](https://patchblox.com/security/data/fix/linux/debian-cve-2026-52944.md) | Jun 25, 2026 |
| Linux | linux Debian 14 | 7.0.12-1 | [DEBIAN-CVE-2026-52944](https://patchblox.com/security/data/fix/linux/debian-cve-2026-52944.md) | Jun 25, 2026 |
| Linux | linux-6.12 Debian 12.15 (bookworm) | 6.12.111-1~deb12u1 | [DEBIAN-CVE-2026-52944](https://patchblox.com/security/data/fix/linux/debian-cve-2026-52944.md) | Jun 25, 2026 |

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Data as of 2026-11-08T19:12:23Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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