In the Linux kernel, the following vulnerability has been resolved: ksmbd: add permission checks for…
Source GCVE Database
Not known to be exploited.
Data as of 10/25/2026, 04:40:13 UTC
No CVSS score from NVD or the CNA
- Exploitation
Not in CISA KEV, no exploitation reported
- EPSS
- 0.4% chance of exploitation in 30 days – higher than 41% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
What to do
AI-suggested
A fix has been implemented in the Linux kernel to add the missing permission checks for FSCTL_DUPLICATE_EXTENTS_TO_FILE in ksmbd. Users should apply the official kernel updates that include this patch. Patch status is not explicitly confirmed in the provided data; therefore, check the Linux kernel vendor advisory for the current remediation guidance and apply updates accordingly.
Description
In the Linux kernel, the following vulnerability has been resolved: ksmbd: add permission checks for FSCTL_DUPLICATE_EXTENTS_TO_FILE The FSCTL_DUPLICATE_EXTENTS_TO_FILE arm of smb2_ioctl() overwrites the destination file's data via vfs_clone_file_range() with neither the share-level KSMBD_TREE_CONN_FLAG_WRITABLE check nor a per-handle fp->daccess check that the other write-bearing arms carry. A client can overwrite destination data on a read-only share, or from a handle opened with only FILE_WRITE_ATTRIBUTES (which still yields an FMODE_WRITE filp). FILE_WRITE_ATTRIBUTES-only destination handle overwrote the file's data via the clone. Add both checks, matching the FSCTL_SET_SPARSE permission fix; require FILE_WRITE_DATA since this writes data.
Impact
Clients could overwrite file data on read-only SMB shares or via handles that should not have write permissions, potentially leading to unauthorized data modification. This could compromise data integrity on affected systems running vulnerable Linux kernel versions with ksmbd enabled.
Summary
The Linux kernel's ksmbd smb2_ioctl() function's FSCTL_DUPLICATE_EXTENTS_TO_FILE operation previously permitted overwriting destination file data via vfs_clone_file_range() without enforcing share-level writable flags or per-handle write access checks. This omission allowed clients to overwrite files on read-only shares or with handles opened with only FILE_WRITE_ATTRIBUTES, which should not permit data writes. The fix introduces both share-level and per-handle permission checks, aligning with the FSCTL_SET_SPARSE permission model, and mandates FILE_WRITE_DATA access for the clone operation.
References
- nvd.nist.gov/vuln/detail/CVE-2026-64399 (opens in a new tab)
- git.kernel.org/stable/c/388e4139db27a9e3612c9d356b826f5b1ff6a9e3 (opens in a new tab)
- git.kernel.org/stable/c/620d133d469295ee7c017ca6aafac335f65c4a5a (opens in a new tab)
- git.kernel.org/stable/c/9b9cf7e65cbeaae1b6636144bacee611cdd7a5d6 (opens in a new tab)
- git.kernel.org/stable/c/baae7b39673ec21073a25e3d14f8feaada01d5df (opens in a new tab)
- git.kernel.org/stable/c/bf460ad5958d506492de4524a656439da3f99c51 (opens in a new tab)
- git.kernel.org/stable/c/c917e4522d251071dde9871b9142d8ea1186ebfe (opens in a new tab)