Out-of-bounds read in Linux kernel - CVE-2026-63909

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Main Vulnerability Database Vulnerabilities #VU138745

Out-of-bounds read in Linux kernel - CVE-2026-63909

Published: July 20, 2026


Vulnerability identifier: #VU138745
CSH Severity: Medium
CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-63909
CWE-ID: CWE-125
Exploitation vector: Remote access
Exploit availability: No public exploit available

Vulnerability details

The vulnerability allows a remote attacker to disclose sensitive information.

The vulnerability exists due to an out-of-bounds read in smb_check_perm_dacl() ACE-walk loops in ksmbd when processing SMB2_CREATE operations with a crafted security descriptor. A remote attacker can send a specially crafted request to disclose sensitive information.

The issue is caused by a transposed bounds check that can leave the loop guard ineffective and permit reading ace->size even when only 0 to 3 bytes remain in the ACE data.


Affected software

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

How to mitigate CVE-2026-63909

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-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

External References

Related Security Bulletins