CVE-2026-64389Network attack vector

SMB session interruption via pre-validation key overwrite

Published Jul 25, 2026 · Updated Jul 25, 2026

Improper authentication in the Linux Kernel allows remote attackers to interrupt SMB sessions via malformed multichannel binding requests. ksmbd_auth_ntlmv2() writes the derived key to sess->sess_key before checking the NT proof, and KEY_XCH rewrites it after the check fails. No credentials or user action are required, but an existing SMB session must be present; repeated corruption can disable that session and its recovery.

CVSS severity8.2
High
EPSS probability0.45%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper authentication in the Linux Kernel allows remote attackers to interrupt SMB sessions via malformed multichannel binding requests. ksmbd_auth_ntlmv2() writes the derived key to sess->sess_key before checking the NT proof, and KEY_XCH rewrites it after the check fails. No credentials or user action are required, but an existing SMB session must be present; repeated corruption can disable that session and its recovery.

The record

CVE
CVE-2026-64389
Published
Jul 25, 2026
Updated
Jul 25, 2026
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
T1499
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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=5.15
  2. Affected versionversion=e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 <89ca7756d5566ba636bb9092cdbe57dab095e136
  3. Affected versionversion=e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 <954d196bebb2b50151cb96454c72dc113b2af1ac
  4. Affected versionversion=e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 <b56400364aed5c34d6e1a0b493081290a5328a9c

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=5.15; version=e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 <89ca7756d5566ba636bb9092cdbe57dab095e136; version=e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 <954d196bebb2b50151cb96454c72dc113b2af1ac; version=e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 <b56400364aed5c34d6e1a0b493081290a5328a9c

Published CVSS scores

8.2kernel.orgCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/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

T1499Endpoint Denial of Service

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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