8.2

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

Modified
AliasesUBUNTU-CVE-2026-64389DEBIAN-CVE-2026-64389
Published 25-07-2026Last modified 30-10-2026

Vulnerability summary

CVE-2026-64389 is a high (CVSS 8.2) vulnerability in linux. EPSS estimates a 0.48% chance of exploitation in the next 30 days, higher than 41.7% of scored vulnerabilities.

Priority
Prioritisesevere

Severe, CVSS 8.2 (CVE.org); no exploitation reported by the 5 checked sources; EPSS 0% (FIRST, 03-11-2026)

Source freshness unavailable

How is this decided?
CVSS score
8.2/10
010
High · v3.1 (CVE.org)
EPSS score
0.48%
0%100%
Low · +0.03 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 15 · Related 13
MGASA-2026-0336MGASA-2026-0337OPENSUSE-SU-2026:11476-1USN-8726-1USN-8726-2USN-8726-3

Timeline

  1. 25-07-2026
    PublishedVulnerability first disclosed.
  2. 30-10-2026
    Last modifiedVulnerability information updated.

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.

CVSS metrics

5 scores · 4 sources · 2 versions

EPSS trend

Probability

0.48%

Chance of exploitation in the next 30 days

Percentile

42%

Versus all other CVEs

30-day change

Increase +0.03 pp

From 0.45% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

No weakness data has been published for this record.

Affected systems

Version check

Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.

Ubuntu157 products
  • linuxAll versions (No fix recorded) | < 7.0.0-31.31
  • linux-allwinner-5.19All versions (No fix recorded)
  • linux-awsAll versions (No fix recorded) | < 7.0.0-1012.12
  • linux-aws-5.0All versions (No fix recorded)
  • linux-aws-5.11All versions (No fix recorded)
Linux2 products
  • linux≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < e589e997bddde0a6f45672dd871cba7b3ff28e17 | ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < a6a951416b55eaf51ea2742f7ba786f240e70137 | ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < f5d74c186bab26a5d5a025305e67edd0888aa34d | ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < b56400364aed5c34d6e1a0b493081290a5328a9c | ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < 89ca7756d5566ba636bb9092cdbe57dab095e136 | ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < 954d196bebb2b50151cb96454c72dc113b2af1ac | 5.15
  • linux_kernel≥ 5.15, < 6.18.40 | ≥ 6.19, < 7.1.4
Debian1 product
  • linuxAll versions (No fix recorded) | < 6.12.115-2 | < 7.1.4-1

3 vendors · 160 products

References

22 links
Show all 22 references