Vulnerability-Lookup

CVE-2026-64389 (GCVE-0-2026-64389)

Vulnerability from cvelistv5 – Published: 2026-07-25 08:50 – Updated: 2026-07-27 05:00

Title

ksmbd: validate NTLMv2 response before updating session key

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 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.

Severity

8.2 (High)


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

Assigner

Linux

References

3 references

URL	Tags
https://git.kernel.org/stable/c/b56400364aed5c34d…
https://git.kernel.org/stable/c/89ca7756d5566ba63…
https://git.kernel.org/stable/c/954d196bebb2b5015…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 , < b56400364aed5c34d6e1a0b493081290a5328a9c (git) Affected: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 , < 89ca7756d5566ba636bb9092cdbe57dab095e136 (git) Affected: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 , < 954d196bebb2b50151cb96454c72dc113b2af1ac (git)
Linux	Linux	Affected: 5.15 Unaffected: 0 , < 5.15 (semver) Unaffected: 6.18.40 , ≤ 6.18.* (semver) Unaffected: 7.1.4 , ≤ 7.1.* (semver) Unaffected: 7.2-rc1 , ≤ * (original_commit_for_fix)

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{
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      "source": "SUSE CSAF VEX",
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      "title": "SUSE CVE CVE-2026-64389",
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}

GHSA-FXVF-VM38-6PXW

Vulnerability from github – Published: 2026-07-25 12:31 – Updated: 2026-07-25 12:31

Details

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.

Show details on source website

JSON

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{
  "affected": [],
  "aliases": [
    "CVE-2026-64389"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-07-25T10:17:22Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: validate NTLMv2 response before updating session key\n\nksmbd_auth_ntlmv2() derives the NTLMv2 session key into\nsess-\u003esess_key before it verifies the NTLMv2 response.\nksmbd_decode_ntlmssp_auth_blob() then continues into KEY_XCH even\nwhen ksmbd_auth_ntlmv2() failed.\n\nWith SMB3 multichannel binding, the failed authentication operates on\nan existing session and the session setup error path does not expire\nbinding sessions. A client can send a binding session setup with a\nbad NT proof and KEY_XCH and still modify sess-\u003esess_key before\nSTATUS_LOGON_FAILURE is returned.\n\nRelevant path:\n\n  smb2_sess_setup()\n    -\u003e conn-\u003ebinding = true\n    -\u003e ntlm_authenticate()\n       -\u003e session_user()\n       -\u003e ksmbd_decode_ntlmssp_auth_blob()\n          -\u003e ksmbd_auth_ntlmv2()\n             -\u003e calc_ntlmv2_hash()\n             -\u003e hmac_md5_usingrawkey(..., sess-\u003esess_key)\n             -\u003e crypto_memneq() returns mismatch\n          -\u003e KEY_XCH arc4_crypt(..., sess-\u003esess_key, ...)\n    -\u003e out_err without expiring the binding session\n\nDerive the base session key into a local buffer and copy it to\nsess-\u003esess_key only after the proof matches. Return immediately on\nauthentication failure so KEY_XCH is only processed after successful\nauthentication.",
  "id": "GHSA-fxvf-vm38-6pxw",
  "modified": "2026-07-25T12:31:33Z",
  "published": "2026-07-25T12:31:33Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-64389"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/89ca7756d5566ba636bb9092cdbe57dab095e136"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/954d196bebb2b50151cb96454c72dc113b2af1ac"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/b56400364aed5c34d6e1a0b493081290a5328a9c"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.

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CVE-2026-64389 (GCVE-0-2026-64389)

GHSA-FXVF-VM38-6PXW

Tags

Sightings

Nomenclature