Linux Kernel up to 6.18.39/7.1.3 Ksmbd ksmbd_auth_ntlmv2 access control

CVSS Meta Temp Score
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CTI Interest Score
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9.5$5k-$25k3.10-

Summaryinfo

A vulnerability was found in Linux Kernel up to 6.18.39/7.1.3 and classified as very critical. Affected by this vulnerability is the function ksmbd_auth_ntlmv2 of the component Ksmbd. Such manipulation leads to access control. This vulnerability is referenced as CVE-2026-64389. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability, which was classified as very critical, has been found in Linux Kernel up to 6.18.39/7.1.3. Affected by this issue is the function ksmbd_auth_ntlmv2 of the component Ksmbd. The manipulation with an unknown input leads to a access control vulnerability. Using CWE to declare the problem leads to CWE-284. The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor. Impacted is confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at git.kernel.org. This vulnerability is handled as CVE-2026-64389 since 07/19/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $5k-$25k (estimation calculated on 07/25/2026). The MITRE ATT&CK project declares the attack technique as T1068.

Upgrading to version 6.18.40, 7.1.4 or 7.2-rc1 eliminates this vulnerability. Applying the patch b56400364aed5c34d6e1a0b493081290a5328a9c/89ca7756d5566ba636bb9092cdbe57dab095e136/954d196bebb2b50151cb96454c72dc113b2af1ac is able to eliminate this problem.

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Productinfo

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Version

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CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 10.0
VulDB Meta Temp Score: 9.5

VulDB Base Score: 10.0
VulDB Temp Score: 9.5
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

AVACAuCIA
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💳💳💳💳💳💳
💳💳💳💳💳💳
VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Access control
CWE: CWE-284 / CWE-266
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.18.40/7.1.4/7.2-rc1
Patch: b56400364aed5c34d6e1a0b493081290a5328a9c/89ca7756d5566ba636bb9092cdbe57dab095e136/954d196bebb2b50151cb96454c72dc113b2af1ac

Timelineinfo

07/19/2026 CVE reserved
07/25/2026 +6 days Advisory disclosed
07/25/2026 +0 days VulDB entry created
07/25/2026 +0 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2026-64389 (🔒)
GCVE (CVE): GCVE-0-2026-64389
GCVE (VulDB): GCVE-100-383240

Entryinfo

Created: 07/25/2026 18:47
Changes: 07/25/2026 18:47 (59)
Complete: 🔍
Cache ID: 216::103

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