What is CVE-2026-64389?

CVE-2026-64389 is a High severity Linux kernel vulnerability with a CVSS score of 8.2 out of 10, affecting Linux kernel versions from 5.15 onward and patched in 6.18.40, 7.1.4 and 7.2. CVE-2026-64389 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.

What is the CVSS score for CVE-2026-64389?

CVE-2026-64389 has a CVSS score of 8.2 out of 10, rated High severity. The vector string is CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H.

Is there a patch available for CVE-2026-64389?

Yes, CVE-2026-64389 has been patched. Fixed versions include 6.18.40, 7.1.4 and 7.2. If you are running Linux kernel 5.15 or later up to the fix versions, apply the relevant patch for your kernel branch.

Is CVE-2026-64389 actively exploited?

CVE-2026-64389 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.

CVE-2026-64389

High

In the Linux kernel, the following vulnerability has been resolved: ksmbd: validate NTLMv2 response before updating session key ksmbd_auth_ntlmv2() derives the NTLMv2 session key into sess->sess_key before it verifies the NTLMv2 response. ksmbd_decode_ntlmssp_auth_blob() then continues into KEY_XCH even when ksmbd_auth_ntlmv2() failed. With SMB3 multichannel binding, the failed authentication operates on an existing session and the session setup error path does not expire binding sessions. A client can send a binding session setup with a bad NT proof and KEY_XCH and still modify sess->sess_key before STATUS_LOGON_FAILURE is returned. Relevant path: smb2_sess_setup() -> conn->binding = true -> ntlm_authenticate() -> session_user() -> ksmbd_decode_ntlmssp_auth_blob() -> ksmbd_auth_ntlmv2() -> calc_ntlmv2_hash() -> hmac_md5_usingrawkey(..., sess->sess_key) -> crypto_memneq() returns mismatch -> KEY_XCH arc4_crypt(..., sess->sess_key, ...) -> out_err without expiring the binding session Derive the base session key into a local buffer and copy it to sess->sess_key only after the proof matches. Return immediately on authentication failure so KEY_XCH is only processed after successful authentication.

Package Linux Kernel

Published 2026-07-25

Last modified 2026-09-04

CVSS version 3.1

Patch available

Yes

CVSS 3.1 score

8.2

out of 10

High

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

Low

Availability

High

Vector string

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H

Affected versions

Linux kernel versions 5.15 and later are affected. Fixed in 6.18.40, 7.1.4, 7.2 and their respective stable series.

Affected from

≥ 5.15

Fixed in

✓ 6.18.40 6.18.x ✓ 7.1.4 7.1.x ✓ 7.2

References

3 total

Kernel Git
https://git.kernel.org/stable/c/89ca7756d5566ba636bb9092cdbe57dab095e136

Patch
Kernel Git
https://git.kernel.org/stable/c/954d196bebb2b50151cb96454c72dc113b2af1ac

Patch
Kernel Git
https://git.kernel.org/stable/c/b56400364aed5c34d6e1a0b493081290a5328a9c

Patch

Details

CVE ID CVE-2026-64389

Severity High

CVSS score 8.2 / 10

CVSS version 3.1

Published 2026-07-25

Modified 2026-09-04

KEV No

Patch

Yes

Package linux

Frequently asked questions

What is CVE-2026-64389?

CVE-2026-64389 is a High severity Linux kernel vulnerability with a CVSS score of 8.2 out of 10 . It affects Linux kernel versions from 5.15 onward and has been patched in 6.18.40, 7.1.4 and 7.2. CVE-2026-64389 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.
What is the CVSS score for CVE-2026-64389?

CVE-2026-64389 has a CVSS score of 8.2 out of 10, rated High severity (CVSS 3.1). The vector string is CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H.
Is there a patch available for CVE-2026-64389?

Yes. CVE-2026-64389 has been patched. Fixed versions include 6.18.40, 7.1.4 and 7.2. If you are running Linux kernel 5.15 or later up to the fix versions, apply the relevant patch for your kernel branch.
Is CVE-2026-64389 actively exploited?

No. CVE-2026-64389 has not been confirmed as actively exploited. It is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.