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NVD / CVE Program· CNA Linux

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

HighCVSS 8.2 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 32/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.48% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: Linux Linux 89ca7756d5566ba636bb9092cdbe57dab095e136, 954d196bebb2b50151cb96454c72dc113b2af1ac, a6a951416b55eaf51ea2742f7ba786f240e70137.

Low priority for now. Upgrade to Linux Linux 89ca7756d5566ba636bb9092cdbe57dab095e136, 954d196bebb2b50151cb96454c72dc113b2af1ac, a6a951416b55eaf51ea2742f7ba786f240e70137 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

Published
Jul 25, 2026
Updated
Oct 30, 2026
EPSS
0.4% · 42th percentile
CWE
—

Report tools

JSON

Action score

32

Monitor

Low priority for now.

CVSS
32 / 40 · 8.2 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.4%

CNA vs NVD score

NVD
—
CNA · Linux
8.2
NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

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  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

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Follow CVE-2026-64389

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  • when exploit code appears or is weaponized
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  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
linuxlinux kernel

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 5.15affected
    • e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 and later · before e589e997bddde0a6f45672dd871cba7b3ff28e17affected · git
    • e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 and later · before a6a951416b55eaf51ea2742f7ba786f240e70137affected · git
    • e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 and later · before f5d74c186bab26a5d5a025305e67edd0888aa34daffected · git
    • e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 and later · before b56400364aed5c34d6e1a0b493081290a5328a9caffected · git
    • e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 and later · before 89ca7756d5566ba636bb9092cdbe57dab095e136affected · git
    • e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 and later · before 954d196bebb2b50151cb96454c72dc113b2af1acaffected · git
    • before 5.15not affected · semver
    • 6.1.191 and later · up to and including 6.1.*not affected · semver
    • 6.6.160 and later · up to and including 6.6.*not affected · semver

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • linux linux kernel5.15 and later · before 6.18.40
  • linux linux kernel6.19 and later · before 7.1.4

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12linuxfrom 0—
Debian:13linuxbefore 6.12.115-26.12.115-2
Debian:14linuxbefore 7.1.4-17.1.4-1

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
    90Now
  • CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe…KEV
    89Now
  • CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
    85Now

Published before and after this one in the same product

  • ← EarlierCVE-2026-64387Jul 25, 2026 · smb: client: fix query directory replay double-free
    39Monitor
  • ← EarlierCVE-2026-64388Jul 25, 2026 · smb/client: fix chown/chgrp with SMB3 POSIX Extensions
    31Monitor
  • Later →CVE-2026-64391Jul 25, 2026 · ksmbd: use opener credentials for ADS I/O
    39Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux89ca7756d5566ba636bb9092cdbe57dab095e136Vendor (CNA)
Linux Linux954d196bebb2b50151cb96454c72dc113b2af1acVendor (CNA)
Linux Linuxa6a951416b55eaf51ea2742f7ba786f240e70137Vendor (CNA)
Linux Linuxb56400364aed5c34d6e1a0b493081290a5328a9cVendor (CNA)
Linux Linuxe589e997bddde0a6f45672dd871cba7b3ff28e17Vendor (CNA)
Linux Linuxf5d74c186bab26a5d5a025305e67edd0888aa34dVendor (CNA)
debian:linux6.12.115-2 · Debian:13Package registry (OSV)
debian:linux7.1.4-1 · Debian:14Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Not on record for this CVE: patch commit or PR link · researcher credit · variant or chain candidate · public bounty program.

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
low · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
Low
Availability impact
High

Weakness class (CWE)

—

CVSS vector

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

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

References

Show all references (5 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records