---
id: CVE-2026-64389
title: |-
  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 respon…
summary: |-
  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 respon…
severity: high
cvss: 8.2
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H'
vendor: linux
product: linux_kernel
affected:
  - 'linux_kernel >= 5.15, < 6.18.40'
  - 'linux_kernel >= 6.19, < 7.1.4'
patched:
  - linux_kernel 7.1.4
published: '2026-07-25'
updated: '2026-09-04'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-64389'
references:
  - url: 'https://git.kernel.org/stable/c/89ca7756d5566ba636bb9092cdbe57dab095e136'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/954d196bebb2b50151cb96454c72dc113b2af1ac'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/b56400364aed5c34d6e1a0b493081290a5328a9c'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
epss: 0.00453
epssPercentile: 0.3673
ingestedAt: '2026-09-05T13:39:57.395Z'
---

## Overview

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.

## Affected

- `linux_kernel >= 5.15, < 6.18.40`
- `linux_kernel >= 6.19, < 7.1.4`

## Remediation

Upgrade past the affected range:

- `linux_kernel 7.1.4`