CVE-2026-64399: In the Linux kernel, the following vulnerability has been resolved: ksmbd: add permission checks for FSCTL_DU

Q: How do I fix CVE-2026-64399?

linux kernel: upgrade to 6.1.178, 6.6.145, 6.12.96, 6.18.39, 7.1.4. Exact commands for each OS are on this page.

Q: Is CVE-2026-64399 being exploited?

CVE-2026-64399 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-64399 affect?

CVE-2026-64399 affects linux kernel. Severity is critical (CVSS 9.8). 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_cl

Q: How urgent is CVE-2026-64399?

Priority 55/100. Critical severity; Remotely exploitable, no login, no user action; On your watchlist

This month

CRITICAL 9.8REMOTEWATCHLISTUPGRADE

CVE-2026-64399 is a critical-severity flaw (CVSS 9.8) affecting linux kernel. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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-on

Why this priority

Critical severity
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 58%)
CISA exploited list	No
Published	2026-07-25
Last modified	2026-09-04

Publisher (CNA): kernel.org · Vendor: linux

Last updated 2026-09-04 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-25 10:17 UTCPublished CVE record published
2026-09-04 14:46 UTCUpdated Record last modified

linux linux kernel UPGRADE

Affected: >= 5.15 and < 6.1.178 · >= 6.2 and < 6.6.145 · >= 6.7 and < 6.12.96 · >= 6.13 and < 6.18.39 · >= 6.19 and < 7.1.4

Fixed in: 6.1.178, 6.6.145, 6.12.96, 6.18.39, 7.1.4

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-64399?

linux kernel: upgrade to 6.1.178, 6.6.145, 6.12.96, 6.18.39, 7.1.4. Exact commands for each OS are on this page.

Is CVE-2026-64399 being exploited?

CVE-2026-64399 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-64399 affect?

CVE-2026-64399 affects linux kernel. Severity is critical (CVSS 9.8). 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_cl

How urgent is CVE-2026-64399?

Priority 55/100. Critical severity; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Linux kernel vulnerabilities

Related CVEs

CVE-2026-63893 HIGH 8.1 UPGRADE In the Linux kernel, the following vulnerability has been resolved: thunderbolt: property: Reject u32 wrap in
CVE-2026-63888 CRITICAL 9.8 UPGRADE In the Linux kernel, the following vulnerability has been resolved: scsi: target: iscsi: Fix CRC overread and
CVE-2026-63885 HIGH 8.8 UPGRADE In the Linux kernel, the following vulnerability has been resolved: drm/gem: fix race between change_handle a
CVE-2026-63884 HIGH 7.8 UPGRADE In the Linux kernel, the following vulnerability has been resolved: drm/i915: Fix potential UAF in TTM object
CVE-2026-63881 HIGH 7.8 UPGRADE In the Linux kernel, the following vulnerability has been resolved: drm/amdkfd: fix a vulnerability of intege

References

← Back to latest CVEs