Out-of-bounds read in Linux kernel - CVE-2026-64138

Vulnerability identifier: #VU138502

CSH Severity: Medium

CVSS v4: 7.1 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-64138

CWE-ID: CWE-125

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote user to cause a denial of service.

The vulnerability exists due to an out-of-bounds read in the ksmbd smbacl.c ACL inheritance logic when processing owner and group SIDs from a parent security descriptor. A remote user can provide a specially crafted parent security descriptor to cause a denial of service.

The issue occurs during ACL inheritance in ksmbd.

Linux kernel
Ubuntu
linux-ibm (Ubuntu package)
linux-azure (Ubuntu package)
linux-aws (Ubuntu package)
linux-nvidia (Ubuntu package)
linux-nvidia-bos (Ubuntu package)

Install security update from vendor's repository.

Linux kernel - update to 7.0 rc3
linux-ibm (Ubuntu package) - addressed in versions 7.0.0-1008.8, 7.0.0-1010.10
linux-azure (Ubuntu package) - addressed in versions 7.0.0-1009.9, 7.0.0-1010.10
linux-aws (Ubuntu package) - addressed in versions 7.0.0-1009.9, 7.0.0-1015.15
linux-nvidia (Ubuntu package) - addressed in versions 7.0.0-1016.16, 7.0.0-1016.16~24.04.1
linux-nvidia-bos (Ubuntu package) - update to 7.0.0-2016.16

• https://git.kernel.org/stable/c/18d8db24b0a5b7be4829238dd4022236df02d421
• https://git.kernel.org/stable/c/1c9d0646a9959752f11ca1080dc1ff26bd1756cb
• https://git.kernel.org/stable/c/69f030cf95488ae1186c72ac8c66fd279664ea7f
• https://git.kernel.org/stable/c/f0e5c9c663badc9982e6941322eef1cb17de0f11

• Out-of-bounds read in Linux kernel smb server
• Ubuntu update for linux-ibm
• Ubuntu update for linux-azure
• Ubuntu update for linux-aws
• Ubuntu update for linux-nvidia-bos
• Ubuntu update for linux-nvidia