CVE-2026-52944
Status: ModifiedMedium (5.5)—
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:
Add both share-level writable check and per-handle access check. Use goto out on error to avoid leaking file references.
Technical details traces, logs and code from the original report
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.
CVSS
- Version: 3.1
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- Base score: 5.5
Exploitation probability (EPSS)
- Probability of exploitation in the next 30 days: 0.12%
- Percentile among all scored CVEs: 2
- Score date: 10/5/2026
EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).
Affected technologies (1)
CWEs
- NVD-CWE-noinfo
References
- https://git.kernel.org/stable/c/3127a884525dc8ca4def73254bfcd3ccef0bf812
- https://git.kernel.org/stable/c/3a9a0a1c38ef90788f5d7c4b29903c8b220f744a
- https://git.kernel.org/stable/c/aef151bcfa494bfe983669de2726734b534adb73
- https://git.kernel.org/stable/c/c5ab11263e3c89aa7989afc5374ef7743e092fd0
- https://git.kernel.org/stable/c/cc57232cae23c0df91b4a59d0f519141ce9b5b02
- https://git.kernel.org/stable/c/de9eb0b44fa9123170e6245b49638e0e453c10f8
- https://git.kernel.org/stable/c/ef664475c1bf1a27d45dae6848ca9c9c4d86853f
Raw JSON (NVD)
Show
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: fix FSCTL permission bypass by adding a permission check for FSCTL_SET_SPARSE\n\nFSCTL_SET_SPARSE in fsctl_set_sparse() modifies the file's sparse\nattribute and saves it through xattr without any permission checks.\n\nThis exposes two issues:\n\n1) A client on a read-only share can change the sparse attribute\n on files it opened, even though the share is read-only.\n Other FSCTL write operations already check\n test_tree_conn_flag(work->tcon, KSMBD_TREE_CONN_FLAG_WRITABLE),\n but FSCTL_SET_SPARSE does not.\n\n2) Even on writable shares, clients without FILE_WRITE_DATA or\n FILE_WRITE_ATTRIBUTES access should not modify the sparse\n attribute. Similar handle-level checks exist in other functions\n but are missing here.\n\nAdd both share-level writable check and per-handle access check.\nUse goto out on error to avoid leaking file references."
}
],
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