VulnerabilityPublished 25 Jul 2026Updated 21 Oct 2026

CVE-2026-64389: Linux kernel · ksmbd: validate NTLMv2 response before updating session key

Affects Linux kernelSource CVE Database V5

Not known to be exploited · CVSS 8.2 High · fixed in f5d74c186bab26a5d5a025305e67edd0888aa34d : patch Linux kernel soon.

Data as of 26 Oct 2026, 14:05 UTC

CVSS 3.1 base score

8.2High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.4% chance of exploitation in 30 days – higher than 40% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in f5d74c186bab26a5d5a025305e67edd0888aa34d, b56400364aed5c34d6e1a0b493081290a5328a9c, a6a951416b55eaf51ea2742f7ba786f240e70137 +2

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: Low
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 25 Jul 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < f5d74c186bab26a5d5a025305e67edd0888aa34d	Fixed in f5d74c186bab26a5d5a025305e67edd0888aa34d
LinuxLinux	Affected ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < b56400364aed5c34d6e1a0b493081290a5328a9c	Fixed in b56400364aed5c34d6e1a0b493081290a5328a9c
LinuxLinux	Affected ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < a6a951416b55eaf51ea2742f7ba786f240e70137	Fixed in a6a951416b55eaf51ea2742f7ba786f240e70137
LinuxLinux	Affected ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < 954d196bebb2b50151cb96454c72dc113b2af1ac	Fixed in 954d196bebb2b50151cb96454c72dc113b2af1ac
LinuxLinux	Affected ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < 89ca7756d5566ba636bb9092cdbe57dab095e136	Fixed in 89ca7756d5566ba636bb9092cdbe57dab095e136
LinuxLinux	Affected =5.15	Fixed in–

Description

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.

References

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