EUVD-2026-38734
GHSA-v762-vr2v-9263
Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
ksmbd is network-exposed via SMB/TCP-445, so AV:N; PR:L reflects required authenticated SMB session; I:L captures unauthorized xattr write; A:H retained for sparse-attribute corruption risk.
Primary rating from NVD.
CVSS VectorNVD
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Lifecycle Timeline
5DescriptionNVD
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:
- 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.
- 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.
AnalysisAI
Unauthorized file attribute modification in the Linux kernel's ksmbd SMB server allows authenticated SMB clients to invoke FSCTL_SET_SPARSE and alter a file's sparse xattr without required permissions, bypassing both share-level and per-handle access controls. Two distinct authorization gaps exist: clients on read-only shares can issue the control code because fsctl_set_sparse() omits the KSMBD_TREE_CONN_FLAG_WRITABLE check that other FSCTL write operations enforce, and clients on writable shares with insufficient handle rights (lacking FILE_WRITE_DATA or FILE_WRITE_ATTRIBUTES) can modify the attribute because per-handle checks are entirely absent. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires an active, authenticated SMB session to a Linux host with the ksmbd kernel module loaded and serving at least one share. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The official CVSS 3.1 score of 5.5 (AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H) rates this as Medium severity, but several signals warrant scrutiny. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker with authenticated access to a ksmbd-served read-only SMB share opens a handle to any file visible on that share and sends a crafted SMB2 IOCTL request bearing the FSCTL_SET_SPARSE control code. Because fsctl_set_sparse() performs no share-writability check, the kernel processes the request and modifies the file's sparse xattr despite the read-only share policy. … |
| Remediation | The primary remediation is to upgrade the Linux kernel to a patched stable release: 6.6.143, 6.18.35, 7.0.12, or 7.1. … Detailed patch versions, workarounds, and compensating controls in full report. |
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