CVE-2026-52944

ksmbd: fix FSCTL permission bypass by adding a permission check for FSCTL_SET_SPARSE

Published Jun 24, 2026 CVSS 3.1 · 5.5 Medium EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Debian DLA Debian DLA DLA-4817-1 linux-6.12 security update
Debian DLA Debian DLA DLA-4841-1 linux security update
Debian DSA Debian DSA DSA-6528-1 linux security update
Ubuntu USN Ubuntu USN USN-8566-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8568-1 Linux kernel (OEM) vulnerabilities
Ubuntu USN Ubuntu USN USN-8569-1 Linux kernel (HWE) vulnerabilities
Ubuntu USN Ubuntu USN USN-8593-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8603-1 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-8618-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8663-1 Linux kernel (NVIDIA) vulnerabilities
Ubuntu USN Ubuntu USN USN-8664-1 Linux kernel (NVIDIA BaseOS) vulnerabilities
Ubuntu USN Ubuntu USN USN-8728-1 Linux kernel (GCP) vulnerabilities
Ubuntu USN Ubuntu USN USN-8728-2 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-8728-3 Linux kernel (Oracle) vulnerabilities
Ubuntu USN Ubuntu USN USN-8903-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8904-1 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-8905-1 Linux kernel (GCP) vulnerabilities
Ubuntu USN Ubuntu USN USN-8906-1 Linux kernel (IBM) vulnerabilities
Ubuntu USN Ubuntu USN USN-8903-2 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8905-2 Linux kernel (GCP) vulnerabilities
Ubuntu USN Ubuntu USN USN-8961-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-9002-1 Linux kernel (NVIDIA Tegra) vulnerabilities
Ubuntu USN Ubuntu USN USN-9025-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-9029-1 Linux kernel (Raspberry Pi) vulnerabilities
Ubuntu USN Ubuntu USN USN-9066-1 Linux kernel (HWE) vulnerabilities
History
Type Values Removed Values Added
Weaknesses CWE-285
CWE-306
Type Values Removed Values Added
Weaknesses CWE-285
CWE-306
Type Values Removed Values Added
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.
Title ksmbd: fix FSCTL permission bypass by adding a permission check for FSCTL_SET_SPARSE
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References
Weaknesses

Sources

Status
PUBLISHED
Assigner
Linux
Published
Updated
Sep 14, 2026, 11:58 AM
Reserved
Jun 9, 2026, 7:44 AM
Status
Modified
Published
Jun 24, 2026, 10:17 AM
Modified
Sep 14, 2026, 12:17 PM
Severity
Public date
Jun 24, 2026, 12:00 AM