Incorrect Implementation of Authentication Algorithm in Linux kernel - CVE-2026-64389

Vulnerability identifier: #VU139576

CSH Severity: Low

CVSS v4: 5.3 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-64389

CWE-ID: CWE-303

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote user to modify session key material.

The vulnerability exists due to improper authentication logic in ksmbd NTLMv2 authentication handling when processing SMB3 multichannel binding session setup requests with KEY_XCH. A remote user can send a binding session setup with a bad NT proof and KEY_XCH to modify session key material.

The issue occurs on an existing session because the failed authentication path does not expire binding sessions.

Linux kernel
Ubuntu
linux (Ubuntu package)
linux-azure (Ubuntu package)
linux-gcp-7.0 (Ubuntu package)
linux-oracle-7.0 (Ubuntu package)
linux-oem-7.0 (Ubuntu package)
linux-azure-7.0 (Ubuntu package)

Install security update from vendor's repository.

Linux kernel - update to 7.0 rc3
linux (Ubuntu package) - addressed in versions 7.0.0-31.31, 7.0.0-31.31.1, 7.0.0-31.31~24.04.1, 7.0.0-1006.7, 7.0.0-1011.11~24.04.1, 7.0.0-1012.12, 7.0.0-1012.12~24.04.1
linux-azure (Ubuntu package) - addressed in versions 7.0.0-1011.11, 7.0.0-1014.14
linux-gcp-7.0 (Ubuntu package) - update to 7.0.0-1011.11~24.04.1
linux-oracle-7.0 (Ubuntu package) - update to 7.0.0-1011.11~24.04.1
linux-oem-7.0 (Ubuntu package) - update to 7.0.0-1013.13
linux-azure-7.0 (Ubuntu package) - update to 7.0.0-1014.14~24.04.1

• https://git.kernel.org/stable/c/89ca7756d5566ba636bb9092cdbe57dab095e136
• https://git.kernel.org/stable/c/954d196bebb2b50151cb96454c72dc113b2af1ac
• https://git.kernel.org/stable/c/b56400364aed5c34d6e1a0b493081290a5328a9c

• Incorrect Implementation of Authentication Algorithm in Linux kernel smb server
• Ubuntu update for linux-oem-7.0
• Ubuntu update for linux
• Ubuntu update for linux-gcp-7.0
• Ubuntu update for linux-oracle-7.0
• Ubuntu update for linux-azure
• Ubuntu update for linux-azure-7.0