CVE-2026-64399Network attack vector

Unauthorized file overwrite via unchecked clone permissions

Published Jul 25, 2026 · Updated Jul 25, 2026

Improper authorization in Linux Kernel ksmbd allows remote attackers to overwrite destination file data through a crafted SMB IOCTL. The FSCTL_DUPLICATE_EXTENTS_TO_FILE arm of smb2_ioctl() calls vfs_clone_file_range() without checking a writable share or FILE_WRITE_DATA on the destination handle. A guest session on a guest-enabled share, or a handle limited to FILE_WRITE_ATTRIBUTES, is sufficient to replace file ranges and corrupt stored data.

CVSS severity9.8
Critical
EPSS probability0.49%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper authorization in Linux Kernel ksmbd allows remote attackers to overwrite destination file data through a crafted SMB IOCTL. The FSCTL_DUPLICATE_EXTENTS_TO_FILE arm of smb2_ioctl() calls vfs_clone_file_range() without checking a writable share or FILE_WRITE_DATA on the destination handle. A guest session on a guest-enabled share, or a handle limited to FILE_WRITE_ATTRIBUTES, is sufficient to replace file ranges and corrupt stored data.

The record

CVE
CVE-2026-64399
Published
Jul 25, 2026
Updated
Jul 25, 2026
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 25, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 25, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <6.1.178
  2. Affected versionversion=0 <6.12.96
  3. Affected versionversion=0 <6.18.39
  4. Affected versionversion=0 <6.6.145
  5. Affected versionversion=0 <7.1.4
  6. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <388e4139db27a9e3612c9d356b826f5b1ff6a9e3
  7. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <620d133d469295ee7c017ca6aafac335f65c4a5a
  8. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <9b9cf7e65cbeaae1b6636144bacee611cdd7a5d6
  9. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <baae7b39673ec21073a25e3d14f8feaada01d5df
  10. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <bf460ad5958d506492de4524a656439da3f99c51
  11. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <c917e4522d251071dde9871b9142d8ea1186ebfe

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=0 <6.1.178; version=0 <6.12.96; version=0 <6.18.39; version=0 <6.6.145; version=0 <7.1.4; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <388e4139db27a9e3612c9d356b826f5b1ff6a9e3; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <620d133d469295ee7c017ca6aafac335f65c4a5a; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <9b9cf7e65cbeaae1b6636144bacee611cdd7a5d6; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <baae7b39673ec21073a25e3d14f8feaada01d5df; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <bf460ad5958d506492de4524a656439da3f99c51; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <c917e4522d251071dde9871b9142d8ea1186ebfe

Published CVSS scores

9.8Linux kernel CNACVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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