CVE-2026-64398: In the Linux kernel, the following vulnerability has been resolved: ksmbd: add a permission check for FSCTL_S

Q: How do I fix CVE-2026-64398?

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-2026-64398 being exploited?

CVE-2026-64398 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-2026-64398 affect?

CVE-2026-64398 affects linux kernel. Severity is high (CVSS 8.1). In the Linux kernel, the following vulnerability has been resolved: ksmbd: add a permission check for FSCTL_SET_ZERO_DATA FSCTL_SET_ZERO_DATA in smb2_ioctl() destroys file data via ksmbd_vfs_zero_data() -> vfs_fallocate(PUNCH_HOLE/ZERO_RA

This month

HIGH 8.1WATCHLISTUPGRADE

CVE-2026-64398 is a high-severity flaw (CVSS 8.1) 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 a permission check for FSCTL_SET_ZERO_DATA FSCTL_SET_ZERO_DATA in smb2_ioctl() destroys file data via ksmbd_vfs_zero_data() -> vfs_fallocate(PUNCH_HOLE/ZERO_RANGE) after checking only the share-level KSMBD_TREE_CONN_FLAG_WRITABLE, with no per-handle access check. A handle opened with only FILE_WRITE_ATTRIBUTES still yields an FMODE_WRITE filp (FILE_WRITE_ATTRIBUTES i

Why this priority

High severity
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	8.1 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.5% (top 60%)
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-2026-64398?

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-2026-64398 being exploited?

CVE-2026-64398 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-2026-64398 affect?

CVE-2026-64398 affects linux kernel. Severity is high (CVSS 8.1). In the Linux kernel, the following vulnerability has been resolved: ksmbd: add a permission check for FSCTL_SET_ZERO_DATA FSCTL_SET_ZERO_DATA in smb2_ioctl() destroys file data via ksmbd_vfs_zero_data() -> vfs_fallocate(PUNCH_HOLE/ZERO_RA

How urgent is CVE-2026-64398?

Priority 43/100. High severity; On your watchlist

Software pages

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References

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