Advisory [CVE-2026-52944] fix FSCTL permission bypass by adding a permission check for FSCTL_SET_SPARSE
This security Red Hat Linux advisory covers CVE-2026-52944.
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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 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.
This vulnerability allows a client to bypass intended permission restrictions by using the FSCTL_SET_SPARSE operation. This can lead to unauthorized changes to file properties.
Red Hat severity: not rated. Weakness: CWE-266.
Red Hat lists Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9 as not affected.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · medium-confidence parse· fetched 9 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · medium-confidence parse· fetched 9 days ago·verify at source
Mitigation
The source record does not include mitigation steps. That is not a statement that no fix exists — read the vendor advisory below for the authoritative guidance.
Official advisory · medium-confidence parse· fetched 9 days ago·verify at source
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