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

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Main Vulnerability Database Vulnerabilities #VU138502

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

Published: July 20, 2026


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

Vulnerability details

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.


Affected software

Linux kernel
Ubuntu
linux (Ubuntu package)
linux-lowlatency (Ubuntu package)
linux-nvidia-tegra (Ubuntu package)
linux-gcp-6.8 (Ubuntu package)
linux-oracle (Ubuntu package)
linux-aws-fips (Ubuntu package)
linux-aws (Ubuntu package)
linux-azure (Ubuntu package)
linux-azure-fips (Ubuntu package)
linux-azure-6.8 (Ubuntu package)
linux-raspi-realtime (Ubuntu package)
linux-ibm (Ubuntu package)
linux-oracle-7.0 (Ubuntu package)
linux-gcp-7.0 (Ubuntu package)
linux-azure-7.0 (Ubuntu package)
linux-nvidia (Ubuntu package)
linux-nvidia-bos (Ubuntu package)

How to mitigate CVE-2026-64138

Install security update from vendor's repository.

Linux kernel - update to 7.0 rc3
linux (Ubuntu package) - addressed in versions 6.8.0-139.139+fips1, 6.8.0-1049.53, 6.8.0-1062.65+fips1, 6.8.0-1062.65.1, 6.8.0-1062.65~22.04.1, 6.8.0-1062.70, 6.8.0-1064.68, 6.8.0-1067.75, 6.8.0-1067.75+fips1, 6.8.1-1059.60, 6.8.1-1059.60~22.04.1
linux-lowlatency (Ubuntu package) - addressed in versions 6.8.0-139.139.1, 6.8.0-139.139.1~22.04.1
linux-nvidia-tegra (Ubuntu package) - update to 6.8.0-1035.38
linux-gcp-6.8 (Ubuntu package) - addressed in versions 6.8.0-1036.37, 6.8.0-1064.65, 6.8.0-1067.75~22.04.1
linux-oracle (Ubuntu package) - addressed in versions 6.8.0-1061.64, 6.8.0-1061.64~22.04.1
linux-aws-fips (Ubuntu package) - update to 6.8.0-1064.67+fips1
linux-aws (Ubuntu package) - addressed in versions 6.8.0-1064.67~22.04.1, 7.0.0-1009.9, 7.0.0-1015.15
linux-azure (Ubuntu package) - addressed in versions 6.8.0-1067.75, 7.0.0-1009.9, 7.0.0-1010.10
linux-azure-fips (Ubuntu package) - update to 6.8.0-1067.75+fips1
linux-azure-6.8 (Ubuntu package) - update to 6.8.0-1067.75~22.04.1
linux-raspi-realtime (Ubuntu package) - update to 6.8.0-2053.55
linux-ibm (Ubuntu package) - addressed in versions 7.0.0-1008.8, 7.0.0-1010.10
linux-oracle-7.0 (Ubuntu package) - update to 7.0.0-1011.11~24.04.1
linux-gcp-7.0 (Ubuntu package) - update to 7.0.0-1011.11~24.04.1
linux-azure-7.0 (Ubuntu package) - update to 7.0.0-1014.14~24.04.1
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

External References

Related Security Bulletins