Out-of-bounds read in Linux kernel - CVE-2026-63909
Published: July 20, 2026
Vulnerability identifier: #VU138745
CSH Severity: Medium
CVSS v4.0: 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/E:U/U:Green
CVE-ID: CVE-2026-63909
CWE-ID: CWE-125
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: Linux Foundation
Affected software:
Linux kernel
Linux kernel
Detailed vulnerability description
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.
How to mitigate CVE-2026-63909
Install security update from vendor's repository.
Sources
- https://git.kernel.org/stable/c/0e60dafe97eca61721f3db456f97d97a80c6c8ae
- https://git.kernel.org/stable/c/0fe08c5776a798f46df1fd74b331be26bdd644d6
- https://git.kernel.org/stable/c/4f7c131d2bdd7cd64b96f60d10be5ea72253f520
- https://git.kernel.org/stable/c/5500ba1d410aed1eded3eb04a76b10cfb4409334
- https://git.kernel.org/stable/c/94215d55b09445993929f4fc966061d61de74929
- https://git.kernel.org/stable/c/d333af32e4451285e427f2d9c29de3a39f6f6d48
- https://git.kernel.org/stable/c/f6324b4240cf0b26a84c33f68a1222d727ff4af2