Improper access control in Linux kernel - CVE-2026-64399

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Main Vulnerability Database Vulnerabilities #VU139569

Improper access control in Linux kernel - CVE-2026-64399

Published: July 27, 2026


Vulnerability identifier: #VU139569
CSH Severity: Medium
CVSS v4: 7.1 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-64399
CWE-ID: CWE-284
Exploitation vector: Remote access
Exploit availability: No public exploit available

Vulnerability details

The vulnerability allows a remote user to overwrite file data.

The vulnerability exists due to improper access control in the FSCTL_DUPLICATE_EXTENTS_TO_FILE arm of smb2_ioctl() when processing SMB ioctl requests that clone file ranges. A remote user can use the operation on a read-only share or with a destination handle lacking FILE_WRITE_DATA permission to overwrite file data.

The issue affects destination files through vfs_clone_file_range() and can be triggered with a handle opened with only FILE_WRITE_ATTRIBUTES.


Affected software

Linux kernel
Ubuntu
linux (Ubuntu package)
linux-azure (Ubuntu package)
linux-gcp-7.0 (Ubuntu package)
linux-oracle-7.0 (Ubuntu package)
linux-oem-7.0 (Ubuntu package)
linux-azure-7.0 (Ubuntu package)

How to mitigate CVE-2026-64399

Install security update from vendor's repository.

Linux kernel - update to 7.0 rc3
linux (Ubuntu package) - addressed in versions 7.0.0-31.31, 7.0.0-31.31.1, 7.0.0-31.31~24.04.1, 7.0.0-1006.7, 7.0.0-1011.11~24.04.1, 7.0.0-1012.12, 7.0.0-1012.12~24.04.1
linux-azure (Ubuntu package) - addressed in versions 7.0.0-1011.11, 7.0.0-1014.14
linux-gcp-7.0 (Ubuntu package) - update to 7.0.0-1011.11~24.04.1
linux-oracle-7.0 (Ubuntu package) - update to 7.0.0-1011.11~24.04.1
linux-oem-7.0 (Ubuntu package) - update to 7.0.0-1013.13
linux-azure-7.0 (Ubuntu package) - update to 7.0.0-1014.14~24.04.1

External References

Related Security Bulletins